gcc

问题 void f () { int a[1]; int b; int c; int d[1]; } I have found that these local variables, for this example, are not pushed on to the stack in order. b and c are pushed in the order of their declaration, but, a and d are grouped together. So the compiler is allocating arrays differently from any other built in type or object. Is this a C/C++ requirement or gcc implementation detail? 回答1: The C standard says nothing about the order in which local variables are allocated. It doesn't even use the

问题 I am learning GCC's extended inline assembly currently. I wrote an A + B function and wants to detect the ZF flag, but things behave strangely. The compiler I use is gcc 7.3.1 on x86-64 Arch Linux. I started from the following code, this code will correctly print the a + b . int a, b, sum; scanf("%d%d", &a, &b); asm volatile ( "movl %1, %0\n" "addl %2, %0\n" : "=r"(sum) : "r"(a), "r"(b) : "cc" ); printf("%d\n", sum); Then I simply added a variable to check flags, it gives me wrong output. int

问题 I am trying to deal with a problem like the following one: Assume that I have a library libxyz.a created from: /* main.c */ int main(void) { int a; } compiled and archived with: gcc -c main.c -o abc.o && ar cr libxyz.a abc.o How do I have to write linker script in order to put abc.o exactly where it is expected to be? I was trying to handle it in such way: /* script.ld */ SEARCH_DIR(.) INPUT(-lxyz) SECTIONS { .text : { xyz:abc(.text) } .data : { xyz:abc(.data) } .bss : { xyz:abc(.bss) } } but

问题 I tried to look at the assembly code for a very simple program. int func(int x) { int z = 1337; return z; } With GCC -O0, every C variable has a memory address that's not optimized away, so gcc spills its register arg: (Godbolt, gcc5.5 -O0 -fverbose-asm) func: pushq %rbp # movq %rsp, %rbp #, movl %edi, -20(%rbp) # x, x movl $1337, -4(%rbp) #, z movl -4(%rbp), %eax # z, D.2332 popq %rbp # ret What is the reason that the function parameter x gets placed on the stack below the local variables?

问题 I tried to look at the assembly code for a very simple program. int func(int x) { int z = 1337; return z; } With GCC -O0, every C variable has a memory address that's not optimized away, so gcc spills its register arg: (Godbolt, gcc5.5 -O0 -fverbose-asm) func: pushq %rbp # movq %rsp, %rbp #, movl %edi, -20(%rbp) # x, x movl $1337, -4(%rbp) #, z movl -4(%rbp), %eax # z, D.2332 popq %rbp # ret What is the reason that the function parameter x gets placed on the stack below the local variables?

问题 I have 2 yocto pkgs that can be successfully compiled with gcc 5.4, cmake 3.6.1 on yocto 2.0.2 but I'm facing the following issue with: gcc 6.3, cmake 3.6.1 on yocto 2.4 . After some research, I observed that yocto changed the sysroot structure (sysroot per package instead of a common sysroot). The error looks like this: CMake Warning at src/mytest/CMakeLists.txt:71 (add_executable): Cannot generate a safe linker search path for target mytest because files in some directories may conflict

问题 I am getting gcc error when trying to install Ta-lib as a global package on my mac. I get an error below: gcc -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I//anaconda/include -arch x86_64 -I//anaconda/include -arch x86_64 -I//anaconda/lib/python3.6/site-packages/numpy/core/include -I/usr/include -I/usr/local/include -I/opt/include -I/opt/local/include -I//anaconda/include/python3.6m -c talib/common.c -o build/temp.macosx-10.7-x86_64-3

问题 I have a simple tagged union of values. The values can either be int64_ts or doubles . I am performing addition on the these unions with the caveat that if both arguments represent int64_t values then the result should also have an int64_t value. Here is the code: #include<stdint.h> union Value { int64_t a; double b; }; enum Type { DOUBLE, LONG }; // Value + type. struct TaggedValue { Type type; Value value; }; void add(const TaggedValue& arg1, const TaggedValue& arg2, TaggedValue* out) {

问题 Well, my colleague is pretty in depth nitpicking about eliminating unnecessarily code instantiations for destructor functions. Still same situation, as mentioned in this question: Very limited space for .text section (less 256 KB) Code base should scale among several targets, including the most limited ones Well known use cases of the code base by means some destructor logic is neccesary to manage object lifetimes or not (for many cases life-time of objects is infinite, unless the hardware is

问题 The title seems convoluted but our test-case is actually a minimal example for a real case. We have code for which we want to choose implementation of a method based on the template parameter. We during clean up we defined conditional enable_if_t with using clause, and as next step wanted to put definition out of line, this produced following code: #include <type_traits> #include <iostream> #include <string> template <typename T> struct A { template <typename U> using is_int_or_float = std: