Hi Everyone,
We took a bug report on some line assembly code
(https://github.com/weidai11/cryptopp/issues/72). I have two questions
at the end on Clang, Apple and ILP32.
The code performs the following:
asm volatile
(
// save ebx in case -fPIC is being used
// TODO: this might need an early clobber on EDI.
# if BOOL_X32 || BOOL_X64
"pushq %%rbx; cpuid; mov %%ebx, %%edi; popq %%rbx"
# else
"push %%ebx; cpuid; mov %%ebx, %%edi; pop %%ebx"
# endif
: "=a" (output[0]), "=D" (output[1]), "=c" (output[2]),
"=d" (output[3])
: "a" (input), "c" (0)
);
BOOL_X32 is set when __ILP32__ is defined. BOOL_X86 is defined when
__i386__ (and friends) is defined. BOOL_X64 is defined when __x86_64__
(and friends) is defined. We set the conditions based on " System V
Application Binary Interface, AMD64 (With LP64 and ILP32 Programming
Models)", http://sites.google.com/site/x32abi/documents/abi.pdf.
The compiler error is:
$ make cpu.o
clang++ -DNDEBUG -g2 -O2 -arch i386 -fPIC -march=native -pipe -c cpu.cpp
cpu.cpp:104:4: error: register %rbx is only available in 64-bit mode
"pushq %%rbx; cpuid; mov %%ebx, %%edi; popq %%rbx"
^
<inline asm>:1:8: note: instantiated into assembly here
pushq %rbx; cpuid; mov %ebx, %edi; popq %rbx
^~~~~
cpu.cpp:104:4: error: register %rbx is only available in 64-bit mode
"pushq %%rbx; cpuid; mov %%ebx, %%edi; popq %%rbx"
^
<inline asm>:1:42: note: instantiated into assembly here
pushq %rbx; cpuid; mov %ebx, %edi; popq %rbx
^~~~
2 errors generated.
It appears Clang sets ILP32 related defines when using -arch i386:
$ clang++ -arch i386 -dM -E - < /dev/null | egrep -i "(86|64|ilp)"
#define _ILP32 1
#define __ILP32__ 1
...
#define __i386 1
#define __i386__ 1
#define i386 1
As far as I know, when using ILP32, we must interact with the stack
using 64-bit values.
My first question is, is _ILP32_ and _i386_ supposed to be defined
together? According to the docs I found, its not an expected/legal
configuration. _ILP32_ and _x86_64_ is an expected/legal
configuration.
My second question is, how should I work around this? Should I special
case Clang on Apple and attempt to push a 32-bit value? Or should I do
something else?
Thanks in advance.
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