This patch adjusts the build system to accept the --with-sysroot configuration flag for the relevant make targets. Use this line to patch it up:. These instructions will place your riscv-linux-gcc tools in the same installation directory as the riscv-gcc tool installed earlier.

This arrangement is the simplest, but if you would like to place them in a different directory, see here. This "linux" target builds riscv-linux-gcc with glibc and the Linux kernel headers. Because we now have to build glibc, it will take much more time. If you don't have the power of a 16 core machine with you, maybe it's time to get a cup of coffee. We are finally poised to bring in the Linux kernel sources. Download the current minor revision of the 3. The -k switch ensures that our.

The Linux kernel is seemingly infinitely configurable. However, with the current development status, there aren't that many devices or options to tweak. However, start with a default configuration that should work out-of-the-box with the ISA simulator. If you want to edit the configuration, you can use a text-based GUI ncurses to edit the configuration:.

Among other things, we have enabled by default procfs, ext2, and the HTIF virtualized devices a block driver and console. In development, it can be very useful to enable "early printk", which will print messages to the console if the kernel crashes very early. You can access this option at "Early printk" in the "Kernel hacking" submenu.

Linux kernel menuconfig interface. Begin building the kernel once you're satisfied with your configuration. This line is no exception. If you want to speed up the process, you can pass the -j [number] option to make. However, there are a few more things to take care of before we boot it.

We currently develop with BusyBox, an unbelievably useful set of utilities that all compile into one multi-use binary. We use BusyBox without source code modifications. In our case, we will use BusyBox 1. Currently, we need it for its init and ash applets, but with bash cross-compiled for RISC-V, there is no longer a need for ash. We will need to change the cross-compiler, set the build to "static" if desired, you can make it dynamic, but you'll have to copy some libraries later.

We will also enable the init , ash , and mount applets. Also, disable job control for ash when the drop down menu for ash 's suboptions appear. My configuration file used to create this example is located here: busybox-riscv.

You can also download it directly using this snippet of code:. Whether or not you want to use the file provided, enter the configuration interface much in the same way as that of the Linux kernel:. BusyBox menuconfig interface. Looks familiar, eh? Once you've finished, make BusyBox. Now we'll need a way for the kernel to access the binary, and we'll use a root disk image for that.

Before we proceed, change back into the directory with the Linux sources. When we initially developed the kernel, we used an initramfs to store our binaries BusyBox in particular.

However, with our HTIF-enabled block device, we can boot off of a root file system proper. In fact, we still make use of the initramfs, but only to set up devices and the symlink to init. Update on June 20, I no longer maintain an up-to-date root filesystem.

Viewed times. I have Ubuntu Old things. Alexander G. Add a comment. Active Oldest Votes. The only solution that worked for me is: Manual installing of. Sign up or log in Sign up using Google. Sign up using Facebook. Learn more.

Installing an older gcc version 3. Asked 4 years, 7 months ago. Active 4 years, 7 months ago. Viewed 51k times. I have gcc 4. I have followed these steps: Downloaded gcc 3. Extracted the tar. OS: Ubuntu Improve this question. Yes, it did.. Thank you ankit and apologies for late reply. Add a comment. Active Oldest Votes. Check your current version by running gcc -v.

Next, You want to install a previous version. For gcc If you initialize every element of an array, then you do not have to specify its size; its size is determined by the number of elements you initialize.

Alternately, if you specify which elements to initialize, then the size of the array is equal to the highest element number initialized, plus one. In that example, only four elements are initialized, but the last one initialized is element number 99, so there are elements.

You can access the elements of an array by specifying the array name, followed by the element index, enclosed in brackets. Remember that the array elements are numbered starting with zero. That assigns the value 5 to the first element in the array, at position zero. You can treat individual array elements like variables of whatever data type the array is made up of. For example, if you have an array made of a structure data type, you can access the structure elements like this:.

You do this by adding an extra set of brackets and array lengths for every additional dimension you want your array to have. For example, here is a declaration for a two-dimensional array that holds five elements in each dimension a two-element array consisting of five-element arrays :. You can use an array of characters to hold a string see String Constants. The array may be built of either signed or unsigned characters. When you declare the array, you can specify the number of elements it will have.

That number will be the maximum number of characters that should be in the string, including the null character used to end the string. If you choose this option, then you do not have to initialize the array when you declare it. Alternately, you can simply initialize the array to a value, and its size will then be exactly large enough to hold whatever string you used to initialize it.

There are two different ways to initialize the array. You can specify of comma-delimited list of characters enclosed in braces, or you can specify a string literal enclosed in double quotation marks.

Note that if you initialize a string using an array of individual characters, then the null character is not guaranteed to be present. It might be, but such an occurrence would be one of chance, and should not be relied upon. After initialization, you cannot assign a new string literal to an array using the assignment operator. For example, this will not work :. However, there are functions in the GNU C library that perform operations including copy on string arrays.

You can also change one character at a time, by accessing individual string elements as you would any other array:. It is possible for you to explicitly state the number of elements in the array, and then initialize it using a string that has more characters than there are elements in the array. This is not a good thing. The larger string will not override the previously specified size of the array, and you will get a compile-time warning.

Since the original array size remains, any part of the string that exceeds that original size is being written to a memory location that was not allocated for it. You can also initialize the first members of the elements of a number array:.

After initialization, you can still access the union members in the array using the member access operator. You put the array name and element number enclosed in brackets to the left of the operator, and the member name to the right. You can also initialize the elements of a structure array:. As with initializing structures which contain structure members, the additional inner grouping braces are optional.

But, if you use the additional braces, then you can partially initialize some of the structures in the array, and fully initialize others:. In that example, the first element of the array has only its x member initialized. Because of the grouping braces, the value 4 is assigned to the x member of the second array element, not to the y member of the first element, as would be the case without the grouping braces.

After initialization, you can still access the structure members in the array using the member access operator. Pointers hold memory addresses of stored constants or variables. For any data type, including both primitive types and custom types, you can create a pointer that holds the memory address of an instance of that type. You declare a pointer by specifying a name for it and a data type. The data type indicates of what type of variable the pointer will hold memory addresses.

To declare a pointer, include the indirection operator see Pointer Operators before the identifier. Here is the general form of a pointer declaration:. Be careful, though: when declaring multiple pointers in the same statement, you must explicitly declare each as a pointer, using the indirection operator:.

You can initialize a pointer when you first declare it by specifying a variable address to store in it. Note the use of the address operator see Pointer Operators , used to get the memory address of a variable.

On the contrary, that would change the value of the variable that the points to, not the value of the pointer itself. If you are so inclined, you can assign pointer values explicitly using literal integers, casting them to the appropriate pointer type.

However, we do not recommend this practice unless you need to have extremely fine-tuned control over what is stored in memory, and you know exactly what you are doing. It would be all too easy to accidentally overwrite something that you did not intend to.

Most uses of this technique are also non-portable. It is important to note that if you do not initialize a pointer with the address of some other existing object, it points nowhere in particular and will likely make your program crash if you use it formally, this kind of thing is called undefined behavior. That example creates a new union type, union numbers , and declares and initializes the first member of a variable of that type named foo. Finally, it declares a pointer to the type union numbers , and gives it the address of foo.

Instead, you have to use the indirect member access operator see Member Access Expressions. Continuing with the previous example, the following example will change the value of the first member of foo :. That example creates a new structure type, struct fish , and declares and initializes a variable of that type named salmon. Finally, it declares a pointer to the type struct fish , and gives it the address of salmon.

Continuing with the previous example, the following example will change the values of the members of salmon :. Now the length and width members in salmon are 5. You can define structures, unions, and enumerations without listing their members or values, in the case of enumerations. Doing so results in an incomplete type. At some time later in your program you will want to complete the type. You do this by defining it as you usually would:.

There are two type qualifiers that you can prepend to your variable declarations which change how the variables may be accessed: const and volatile. In addition to helping to prevent accidental value changes, declaring variables with const can aid the compiler in code optimization. You might use volatile variables to store data that is updated via callback functions or signal handlers. Sequence Points and Signal Delivery.

There are four storage class specifiers that you can prepend to your variable declarations which change how the variables are stored in memory: auto , extern , register , and static. You use auto for variables which are local to a function, and whose values should be discarded upon return from the function in which they are declared.

This is the default behavior for variables declared within functions. You cannot use the address-of operator to obtain the address of a variable declared with register. This means that you cannot refer to the elements of an array declared with storage class register.

In fact the only thing you can do with such an array is measure its size with sizeof. GCC normally makes good choices about which values to hold in registers, and so register is not often used.

This is known as static storage duration. You can also declare variables or functions at the top level that is, not inside a function to be static ; such variables are visible global to the current source file but not other source files. This gives an unfortunate double meaning to static ; this second meaning is known as static linkage. Two functions or variables having static linkage in separate files are entirely separate; neither is visible outside the file in which it is declared.

Uninitialized variables that are declared as extern are given default values of 0 , 0. Uninitialized variables that are declared as auto or register including the default usage of auto are left uninitialized, and hence should not be assumed to hold any particular value. You cannot initialize a variable in an extern declaration, as no space is actually allocated during the declaration. You must make both an extern declaration typically in a header file that is included by the other source files which need to access the variable and a non- extern declaration which is where space is actually allocated to store the variable.

The extern declaration may be repeated multiple times. See Program Structure and Scope , for related information. Sometimes it is convenient to give a new name to a type. You can do this using the typedef statement.

See The typedef Statement , for more information. An expression consists of at least one operand and zero or more operators. Operands are typed objects such as constants, variables, and function calls that return values. Innermost expressions are evaluated first. Then 12 is subtracted from 13 , resulting in 1.

Finally, 1 is multiplied by 2 , resulting in 2. The outermost parentheses are completely optional. An operator specifies an operation to be performed on its operand s. Operators may have one, two, or three operands, depending on the operator. Assignment operators store values in variables. C provides several variations of assignment operators. Note that, unlike the other assignment operators described below, you can use the plain assignment operator to store values of a structure type.

Compound assignment operators perform an operation involving both the left and right operands, and then assign the resulting expression to the left operand. Here is a list of the compound assignment operators, and a brief description of what they do:. Subtract the right operand from the left operand, and then assign the result of the subtraction to the left operand.

Multiply the two operands together, and then assign the result of the multiplication to the left operand. Divide the left operand by the right operand, and assign the result of the division to the left operand. Perform modular division on the two operands, and assign the result of the division to the left operand. Perform a left shift operation on the left operand, shifting by the number of bits specified by the right operand, and assign the result of the shift to the left operand.

Perform a right shift operation on the left operand, shifting by the number of bits specified by the right operand, and assign the result of the shift to the left operand. Perform a bitwise conjunction operation on the two operands, and assign the result of the operation to the left operand. Performs a bitwise exclusive disjunction operation on the two operands, and assign the result of the operation to the left operand. Performs a bitwise inclusive disjunction operation on the two operands, and assign the result of the operation to the left operand.

Since there are no side effects wrought by evaluating the variable x as an lvalue, the above code produces the same result as:. The operand must be a either a variable of one of the primitive data types, a pointer, or an enumeration variable.

You can apply the increment operator either before or after the operand. Note that incrementing a pointer only makes sense if you have reason to believe that the new pointer value will be a valid memory address. A prefix increment adds 1 before the operand is evaluated. A postfix increment adds 1 after the operand is evaluated.

In the previous examples, changing the position of the operator would make no difference. However, there are cases where it does make a difference:. C provides operators for standard arithmetic operations: addition, subtraction, multiplication, and division, along with modular division and negation. Usage of these operators is straightforward; here are some examples:. However, if either operand is negative, the direction of rounding is implementation-defined. Signed Integer Division for information about overflow in signed integer division.

The operands must be expressions of a primitive data type. Modular division returns the remainder produced after performing integer division on the two operands. The operands must be of a primitive integer type. If the operand you use with the negative operator is of an unsigned data type, then the result cannot negative, but rather is the maximum value of the unsigned data type, minus the value of the operand.

Many systems use twos-complement arithmetic, and on such systems the most negative value a signed type can hold is further away from zero than the most positive value. For example, on one platform, this program:. Numeric values are assumed to be positive unless explicitly made negative, so this operator has no effect on program operation.

The operand must be an expression of a complex number type. You use the comparison operators to determine how two operands relate to each other: are they equal to each other, is one larger than the other, is one smaller than the other, and so on.

When you use any of the comparison operators, the result is either 1 or 0, meaning true or false, respectively. In the following code examples, the variables x and y stand for any two expressions of arithmetic types, or pointers. The result is 1 if the operands are equal, and 0 if the operands are not equal. The not-equal-to operator! The result is 1 if the operands are not equal, and 0 if the operands are equal.

Comparing floating-point values for exact equality or inequality can produce unexpected results. Real Number Types for more information. You can compare function pointers for equality or inequality; the comparison tests if two function pointers point to the same function or not. Beyond equality and inequality, there are operators you can use to test if one value is less than, greater than, less-than-or-equal-to, or greater-than-or-equal-to another value.

Here are some code samples that exemplify usage of these operators:. Logical operators test the truth value of a pair of operands. Any nonzero expression is considered true in C, while an expression that evaluates to zero is considered false.

If the first expression is false, then the second expression is not evaluated. The logical disjunction operator tests if at least one of two expressions it true. If the first expression is true, then the second expression is not evaluated. You can prepend a logical expression with a negation operator! Since the second operand in a logical expression pair is not necessarily evaluated, you can write code with perhaps unintuitive results:. If foo is ever zero, then not only would bar not be called, but x would not be incremented.

If you intend to increment x regardless of the value of foo , you should do so outside of the conjunction expression. The second operand denotes the number of bit places to shift. Bits shifted off the left side of the value are discarded; new bits added on the right side will all be 0. Bits shifted off the right side are discarded; new bits added on the left side are usually 0, but if the first operand is a signed negative value, then the added bits will be either 0 or whatever value was previously in the leftmost bit position.

You can use the shift operators to perform a variety of interesting hacks. For example, given a date with the day of the month numbered as d , the month numbered as m , and the year y , you can store the entire date in a single number x :. You can then extract the original day, month, and year out of x using a combination of shift operators and modular division:.

C provides operators for performing bitwise conjunction, inclusive disjunction, exclusive disjunction, and negation complement. Biwise conjunction examines each bit in its two operands, and when two corresponding bits are both 1, the resulting bit is 1. All other resulting bits are 0. Here is an example of how this works, using binary numbers:. Bitwise inclusive disjunction examines each bit in its two operands, and when two corresponding bits are both 0, the resulting bit is 0.

All other resulting bits are 1. Bitwise exclusive disjunction examines each bit in its two operands, and when two corresponding bits are different, the resulting bit is 1.

In C, you can only use these operators with operands of an integer or character type, and for maximum portability, you should only use the bitwise negation operator with unsigned integer types. Here are some examples of using these operators in C code:. Function pointers and data pointers are not compatible, in the sense that you cannot expect to store the address of a function into a data pointer, and then copy that into a function pointer and call it successfully.

See The goto Statement. This is called dereferencing the pointer. You can use the sizeof operator to obtain the size in bytes of the data type of its operand. The operand may be an actual type specifier such as int or float , as well as any valid expression. When the operand is a type name, it must be enclosed in parentheses. The sizeof operator can be used to automatically compute the number of elements in an array:. There are two cases where this technique does not work. The second is where the array is in fact a function parameter see Function Parameters.

You can use a type cast to explicitly cause an expression to be of a specified data type. A type cast consists of a type specifier enclosed in parentheses, followed by an expression. To ensure proper casting, you should also enclose the expression that follows the type specifier in parentheses.

In that example, since y and z are both integers, integer division is performed, and even though x is a floating-point variable, it receives the value 2. To fix this problem, you need to convert one of the operands to a floating-point type before the division takes place:. Type casting only works with scalar types that is, integer, floating-point or pointer types.

Therefore, this is not allowed:. You can access array elements by specifying the name of the array, and the array subscript or index, or element number enclosed in brackets.

This means that many uses of an array name are equivalent to a pointer expression. It also means that you cannot subscript an array having the register storage class. You use the comma operator , to separate two ostensibly related expressions. For instance, the first expression might produce a value that is used by the second expression:.