On Mon, 2017-08-21 at 15:39 +0200, Mason wrote: > On 19/08/2017 09:10, Andrew Makhorin wrote: > > > The document "System V ABI: Intel386 Architecture Processor Supplement" > > says that contents of %ebx, %esi, and %edi must be preserved for the > > caller. Does GCC for 32-bit GNU/Linux and for 32-bit Cygwin conform to > > this ABI? If not, how to determine which registers are expected to be > > saved by calling C functions? Thank you for your answer. > > (NB: GCC supports dozens of platforms) > > You seem to be interested in the x86 "cdecl" ABI. > > https://en.wikipedia.org/wiki/X86_calling_conventions#cdecl The C Standard says nothing about calling conventions, so I meant that one that is used by default (which is probably cdecl). > > I think the SysV and Microsoft ABI are close, but may differ > over details, e.g. returning structs. I asked my question, because GCC doesn't seem to follow System V ABI. In the following example %ebx, %esi, and %edi are not preserved being clobbered by the generated code. mao@corvax:~/Desktop/foo$ cat foo.c int foo(int x[], int y[], int z[], int i, int j, int k) { int t; t = (x[i+j] + y[j+k] + 2) * (z[i+j+k] + 1) * (z[k+1] + 2); return t; } mao@corvax:~/Desktop/foo$ gcc -c -O2 -save-temps foo.c mao@corvax:~/Desktop/foo$ cat foo.s .file "foo.c" .text .p2align 4,,15 .globl foo .type foo, @function foo: .LFB0: .cfi_startproc subl $12, %esp .cfi_def_cfa_offset 16 movl 32(%esp), %eax movl 36(%esp), %edx movl %ebx, (%esp) .cfi_offset 3, -16 movl 28(%esp), %ebx movl %esi, 4(%esp) movl 24(%esp), %ecx movl %edi, 8(%esp) .cfi_offset 6, -12 .cfi_offset 7, -8 movl 20(%esp), %edi leal (%eax,%edx), %esi addl %eax, %ebx movl 16(%esp), %eax movl (%eax,%ebx,4), %eax addl %edx, %ebx movl (%ecx,%ebx,4), %ebx addl (%edi,%esi,4), %eax movl 4(%ecx,%edx,4), %edx movl 4(%esp), %esi addl $1, %ebx addl $2, %eax movl 8(%esp), %edi imull %ebx, %eax movl (%esp), %ebx addl $12, %esp .cfi_restore 7 .cfi_restore 6 .cfi_restore 3 .cfi_def_cfa_offset 4 addl $2, %edx imull %edx, %eax ret .cfi_endproc .LFE0: .size foo, .-foo .ident "GCC: (Debian 4.7.2-5) 4.7.2" .section .note.GNU-stack,"",@progbits mao@corvax:~/Desktop/foo$ gcc --version gcc (Debian 4.7.2-5) 4.7.2
