Re: fat_init violates host ABI on Win64

[Niels Möller]

I wonder if one could use some m4 macrology to reduce clutter. Maybe
one macro for the pattern

IFSTD(` sub $8, %rsp')
IFDOS(` sub $40, %rsp   ')
ASSERT(nz, `test $15, %rsp')
CALL(   mpn_add_n)
IFSTD(` add $8, %rsp')
IFDOS(` add $40, %rsp   ')

used when it's known that rsp = 8 (mod 16), and another one when it's
known that rsp = 0 (mod 16).

There seems to be a few uses of CALL that want to do this differently,
though, e.g., gcd_1.asm, maybe it would also help to move (and rename)
its conditional definition of STACK_ALLOC.

/Niels

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Re: fat_init violates host ABI on Win64

[Torbjörn Granlund]

Nicolas Hake  writes:

  the Windows x64 ABI requires callers to allocate a 32 byte "parameter
  area" before calling into a function, which the callee is allowed to
  use as it pleases[1]. fat_init does not do this before calling
  __gmpn_cpuvec_init, thus violating the ABI.
  
Right; apparently we're aware of this as such allocations are performed
in most cases in GMP.  There seem to be 5 forgotten places, the one you
found and 4 more.

  I'm not sure whether MSVC is a supported compiler (I assume it isn't,
  because --enable-fat requires support for variable-length arrays,
  which MSVC will not compile in C mode), but it's possible that other
  compilers may also use the parameter area as a scratch space, or even
  that gcc/clang start using it in future releases.
  
We should follow the ABI, of course.

Where do we (unconditionally) rely on variable-length arrays?

While such arrays are in the C standard since 18 years, it is missing
from C++.

  Attached patch solves this problem by just allocating 32 bytes of
  stack space before calling __gmpn_cpuvec_init, and discarding them
  afterwards.
  
Thanks.  Here is a slightly different patch:

diff -Nrc2 gmp-main.253deadf9fc8/mpn/x86_64/divrem_2.asm 
gmp-main/mpn/x86_64/divrem_2.asm
*** gmp-main.253deadf9fc8/mpn/x86_64/divrem_2.asm   Tue Apr 25 20:52:18 2017
--- gmp-main/mpn/x86_64/divrem_2.asmTue Apr 25 20:52:18 2017
***
*** 101,106 
--- 101,108 
  IFSTD(`   mov %r11, %rdi  ')
  IFDOS(`   mov %r11, %rcx  ')
+ IFDOS(`   sub $32, %rsp   ')
ASSERT(nz, `test $15, %rsp')
CALL(   mpn_invert_limb)
+ IFDOS(`   add $32, %rsp   ')
pop %r11
pop %r10
diff -Nrc2 gmp-main.253deadf9fc8/mpn/x86_64/fat/fat_entry.asm 
gmp-main/mpn/x86_64/fat/fat_entry.asm
*** gmp-main.253deadf9fc8/mpn/x86_64/fat/fat_entry.asm  Tue Apr 25 20:52:18 2017
--- gmp-main/mpn/x86_64/fat/fat_entry.asm   Tue Apr 25 20:52:18 2017
***
*** 168,172 
--- 168,174 
push%r9
push%rax
+ IFDOS(`   sub $32, %rsp   ')
CALL(   __gmpn_cpuvec_init)
+ IFDOS(`   add $32, %rsp   ')
pop %rax
pop %r9
diff -Nrc2 gmp-main.253deadf9fc8/mpn/x86_64/mod_1_1.asm 
gmp-main/mpn/x86_64/mod_1_1.asm
*** gmp-main.253deadf9fc8/mpn/x86_64/mod_1_1.asmTue Apr 25 20:52:18 2017
--- gmp-main/mpn/x86_64/mod_1_1.asm Tue Apr 25 20:52:18 2017
***
*** 199,204 
--- 199,206 
  IFSTD(`   mov %r12, %rdi  ')  C pass parameter
  IFDOS(`   mov %r12, %rcx  ')  C pass parameter
+ IFDOS(`   sub $32, %rsp   ')
ASSERT(nz, `test $15, %rsp')
CALL(   mpn_invert_limb)
+ IFDOS(`   add $32, %rsp   ')
neg %r12
mov %r12, %r8
diff -Nrc2 gmp-main.253deadf9fc8/mpn/x86_64/mod_1_2.asm 
gmp-main/mpn/x86_64/mod_1_2.asm
*** gmp-main.253deadf9fc8/mpn/x86_64/mod_1_2.asmTue Apr 25 20:52:18 2017
--- gmp-main/mpn/x86_64/mod_1_2.asm Tue Apr 25 20:52:18 2017
***
*** 184,189 
--- 184,191 
  IFSTD(`   mov %r12, %rdi  ')  C pass parameter
  IFDOS(`   mov %r12, %rcx  ')  C pass parameter
+ IFDOS(`   sub $32, %rsp   ')
ASSERT(nz, `test $15, %rsp')
CALL(   mpn_invert_limb)
+ IFDOS(`   add $32, %rsp   ')
mov %r12, %r8
mov %rax, %r11
diff -Nrc2 gmp-main.253deadf9fc8/mpn/x86_64/mod_1_4.asm 
gmp-main/mpn/x86_64/mod_1_4.asm
*** gmp-main.253deadf9fc8/mpn/x86_64/mod_1_4.asmTue Apr 25 20:52:18 2017
--- gmp-main/mpn/x86_64/mod_1_4.asm Tue Apr 25 20:52:18 2017
***
*** 191,196 
--- 191,198 
  IFSTD(`   mov %r12, %rdi  ')  C pass parameter
  IFDOS(`   mov %r12, %rcx  ')  C pass parameter
+ IFDOS(`   sub $32, %rsp   ')
ASSERT(nz, `test $15, %rsp')
CALL(   mpn_invert_limb)
+ IFDOS(`   add $32, %rsp   ')
mov %r12, %r8
mov %rax, %r11


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