llvm dev - Oct 2013 - [LLVMdev] How to use clang -intergrated-as to compile cross-(os/target) assembly file.

2013/10/23 Reid Kleckner <rnk at google.com>
> I don't think we should attempt to mangle symbols declared in assembly
> source files.  If you're writing assembly, you will need to handle ABI
>
Sorry for the  unclear statements, I didn't means the assembler to mangle
symbols declared in assembly source files, I means directly use assembly
directive to choice which symbol should be used. The compiler just need to
follow the directive.
For example, in assembly files, there is a directive
https://sourceware.org/binutils/docs-2.23.1/as/If.html#If
to act like C macro #ifdef #if, so i wanna to know how to use this
directive to detect if it's target to x86/win32. if that's true, then I
can
control which code to be generate.
> portability, including the _ prefix on win32 x86.
>
>
> clang will run the C preprocessor for you if you use the .S file suffix
> (case matters).
>
> On Tue, Oct 22, 2013 at 7:08 AM, 罗勇刚(Yonggang Luo) <luoyonggang at
gmail.com>wrote:
>
>> For example, I execute the following command sequences:
>>
>> H:\CI\bld\compilers\musl\src\math\i386>type sqrt.s
>> #.globl _sqrt
>> .global sqrt
>> #.type sqrt, at function
>> #_sqrt:
>> sqrt:   fldl 4(%esp)
>>         fsqrt
>>         fstsw %ax
>>         sub $12,%esp
>>         fld %st(0)
>>         fstpt (%esp)
>>         mov (%esp),%ecx
>>         and $0x7ff,%ecx
>>         cmp $0x400,%ecx
>>         jnz 1f
>>         and $0x200,%eax
>>         sub $0x100,%eax
>>         sub %eax,(%esp)
>>         fstp %st(0)
>>         fldt (%esp)
>> 1:      add $12,%esp
>>         fstpl 4(%esp)
>>         fldl 4(%esp)
>>         ret
>>
>> H:\CI\bld\compilers\musl\src\math\i386>type sqrt.c
>> float __cdecl sqrt(float z)
>> {
>>     return 0.0;
>> }
>> H:\CI\bld\compilers\musl\src\math\i386>clang  -integrated-as -c -v
>> --target=i686
>> -pc-win32 sqrt.s
>> clang version 3.4 (trunk)
>> Target: i686-pc-win32
>> Thread model: posix
>>  "C:\Program Files (x86)\LLVM 3.4.svn\bin\clang.exe" -cc1as
-triple
>> i686-pc-win3
>> 2 -filetype obj -main-file-name sqrt.s -target-cpu pentium4
>> -fdebug-compilation-
>> dir "H:\\CI\\bld\\compilers\\musl\\src\\math\\i386"
-dwarf-debug-producer
>> clang
>> version 3.4 (trunk) -o sqrt.o sqrt.s
>>
>> H:\CI\bld\compilers\musl\src\math\i386>llvm-objdump -s -r -t sqrt.o
>>
>> sqrt.o: file format COFF-i386
>>
>> Contents of section .text:
>>  0000 dd442404 d9fa9bdf e083ec0c d9c0db3c  .D$............<
>>  0010 248b0c24 81e1ff07 000081f9 00040000  $..$............
>>  0020 75122500 0200002d 00010000 290424dd  u.%....-....).$.
>>  0030 d8db2c24 83c40cdd 5c2404dd 442404c3  ..,$....\$..D$..
>> SYMBOL TABLE:
>> [ 0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
>> AUX scnlen 0x40 nreloc 0 nlnno 0 checksum 0x0 assoc 1 comdat 0
>> [ 2](sec  1)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 sqrt
>>
>> H:\CI\bld\compilers\musl\src\math\i386>clang --target=i686-pc-win32
-c
>>  sqrt.c
>> sqrt.c:1:15: warning: incompatible redeclaration of library function
>> 'sqrt'
>>       [-Wincompatible-library-redeclaration]
>> float __cdecl sqrt(float z)
>>               ^
>> sqrt.c:1:15: note: 'sqrt' is a builtin with type 'double
(double)'
>> 1 warning generated.
>>
>> H:\CI\bld\compilers\musl\src\math\i386>llvm-objdump -s -r -t sqrt.o
>>
>> sqrt.o: file format COFF-i386
>>
>> Contents of section .text:
>>  0000 5589e583 ec08f30f 1045080f 57c9f30f  U........E..W...
>>  0010 1145fcd9 eef30f11 4df883c4 085dc3    .E......M....].
>> SYMBOL TABLE:
>> [ 0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
>> AUX scnlen 0x1f nreloc 0 nlnno 0 checksum 0x0 assoc 1 comdat 0
>> [ 2](sec -1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000001 @feat.00
>> [ 3](sec  1)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 _sqrt
>>
>> H:\CI\bld\compilers\musl\src\math\i386>
>> H:\CI\bld\compilers\musl\src\math\i386>clang  -integrated-as -c -v
>> --target=amd6
>> 4-pc-win32 sqrt.s
>> clang version 3.4 (trunk)
>> Target: amd64-pc-win32
>> Thread model: posix
>>  "C:\Program Files (x86)\LLVM 3.4.svn\bin\clang.exe" -cc1as
-triple
>> amd64-pc-win
>> 32 -filetype obj -main-file-name sqrt.s -target-cpu x86-64
>> -fdebug-compilation-d
>> ir "H:\\CI\\bld\\compilers\\musl\\src\\math\\i386"
-dwarf-debug-producer
>> clang v
>> ersion 3.4 (trunk) -o sqrt.o sqrt.s
>>
>> H:\CI\bld\compilers\musl\src\math\i386>llvm-objdump -s -r -t sqrt.o
>>
>> sqrt.o: file format COFF-x86-64
>>
>> Contents of section .text:
>>  0000 67dd4424 04d9fa9b dfe083ec 0cd9c067  g.D$...........g
>>  0010 db3c2467 8b0c2481 e1ff0700 0081f900  .<$g..$.........
>>  0020 04000075 14250002 00002d00 01000067  ...u.%....-....g
>>  0030 290424dd d867db2c 2483c40c 67dd5c24  ).$..g.,$...g.\$
>>  0040 0467dd44 2404c3                      .g.D$..
>> SYMBOL TABLE:
>> [ 0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
>> AUX scnlen 0x47 nreloc 0 nlnno 0 checksum 0x0 assoc 1 comdat 0
>> [ 2](sec  1)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 sqrt
>>
>> H:\CI\bld\compilers\musl\src\math\i386>clang --target=amd64-pc-win32
-c
>>  sqrt.c
>> sqrt.c:1:15: warning: incompatible redeclaration of library function
>> 'sqrt'
>>       [-Wincompatible-library-redeclaration]
>> float __cdecl sqrt(float z)
>>               ^
>> sqrt.c:1:15: note: 'sqrt' is a builtin with type 'double
(double)'
>> 1 warning generated.
>>
>> H:\CI\bld\compilers\musl\src\math\i386>llvm-objdump -s -r -t sqrt.o
>>
>> sqrt.o: file format COFF-x86-64
>>
>> Contents of section .text:
>>  0000 554889e5 50f30f11 45fc0f57 c04883c4  UH..P...E..W.H..
>>  0010 085dc3                               .].
>> SYMBOL TABLE:
>> [ 0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .text
>> AUX scnlen 0x13 nreloc 0 nlnno 0 checksum 0x0 assoc 1 comdat 0
>> [ 2](sec  1)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x00000000 sqrt
>>
>> H:\CI\bld\compilers\musl\src\math\i386>
>>
>> *
>> *
>> *My problem is:*
>>
>> Because C __cdecl calling convention vary on x86/amd64 architecture
under
>> win32.
>> for example, the sqrt function in is expressed as
>> float __cdecl sqrt(float)
>>
>> but in the compiled object file, the final COFF symbol table:
>> on x86/win32(i686-pc-win32), it's named with "*_sqrt*"
>> on amd64/win32(amd64-pc-win32), it's named with "*sqrt*"
>>
>>
>>
>> on linux(*-pc-linux), in ELF symbol table, it's named with
"*sqrt*",
>>
>>
>> So I want to control the function name in assembly file, by the means
of
>> Assembly macros,
>> but I don't know LLVM-MC support which kinds of macros to control
the
>> assembly directives so that I can unified the assembly function name
can
>> match the c function name  in object symbol table under different
>> CPU(x86/x64) and different OS(Win32/Linux/MacOS).
>> The simplest way is to duplicate the function name is to duplicate the
>> function name in two form:
>> .globl _sqrt
>> .global sqrt
>> #.type sqrt, at function
>> _sqrt:
>> sqrt:   fldl 4(%esp)
>> But that will leading redundant object symbol name.
>> besides, the* .type *didn't support under COFF symbol table, so how
did
>> I use assembly macro to comment it out when we are targeting COFF
object
>> but reserved when we are targeting ELF.
>> didn't know if Mach-O support for this directive.
>>
>> --
>>          此致
>> 礼
>> 罗勇刚
>> Yours
>>     sincerely,
>> Yonggang Luo
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>

-- 
         此致
礼
罗勇刚
Yours
    sincerely,
Yonggang Luo
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> Sorry for the  unclear statements, I didn't means the assembler to
mangle
> symbols declared in assembly source files, I means directly use assembly
> directive to choice which symbol should be used. The compiler just need to
> follow the directive.
> For example, in assembly files, there is a directive
> https://sourceware.org/binutils/docs-2.23.1/as/If.html#If
> to act like C macro #ifdef #if, so i wanna to know how to use this
directive
> to detect if it's target to x86/win32. if that's true, then I can
control
> which code to be generate.
>>

I don't think there is anything in plain .s files. In .S files you can
use any of the C predefined macros, in particular,
__USER_LABEL_PREFIX__ might be what you want.

Cheers,
Rafael

2013/10/23 Rafael Espíndola <rafael.espindola at gmail.com>
> > Sorry for the  unclear statements, I didn't means the assembler to
mangle
> > symbols declared in assembly source files, I means directly use
assembly
> > directive to choice which symbol should be used. The compiler just
need
> to
> > follow the directive.
> > For example, in assembly files, there is a directive
> > https://sourceware.org/binutils/docs-2.23.1/as/If.html#If
> > to act like C macro #ifdef #if, so i wanna to know how to use this
> directive
> > to detect if it's target to x86/win32. if that's true, then I
can control
> > which code to be generate.
> >>
>
>
> I don't think there is anything in plain .s files. In .S files you can
> use any of the C predefined macros, in particular,
> __USER_LABEL_PREFIX__ might be what you want.
>
Thanks, Rafael, this is acceptable if GCC/binutils also support for this, I
want to keep compatible with GCC/binutils,
besides, is there any command option to force use C predefined macros?
because use .S is too tricky.
>
> Cheers,
> Rafael
>


-- 
         此致
礼
罗勇刚
Yours
    sincerely,
Yonggang Luo
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