https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71216
Bug ID: 71216
Summary: Incorrect PPC assembly due to inserted .machine
pseudo-op
Product: gcc
Version: 6.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at jbirnbaum dot com
Target Milestone: ---
This report concerns rs6000_file_start() in config/rs6000/rs6000.c as modified
by r219854
I'm working with the PowerPC 405 but I believe this affects a number of
different chips.
GCC version info:
Target: powerpc-softfloat-linux
Configured with: ../gcc-6.1.0/configure --prefix=/toolchains/gcc-6.1.0-powerpc
--build=i386-pc-linux-gnu --host=i386-pc-linux-gnu
--target=powerpc-softfloat-linux --enable-languages=c,c++ --disable-nls
--without-headers --disable-__cxa_atexit
Thread model: posix
gcc version 6.1.0 (GCC)
Simple C file used for testing:
int main ()
{
unsigned tcr = 5;
__asm__ volatile (
" mttcr %0 \n"
: /* no output */
: "r"( tcr )
);
return 0;
}
Compiled using powerpc-softfloat-linux-gcc -mcpu=405 -mregnames -nostdlib
-nodefaultlibs filename.c
objdump -d yields:
a.out: file format elf32-powerpc
Disassembly of section .text:
10000074 <main>:
10000074: 94 21 ff e0 stwu r1,-32(r1)
10000078: 93 e1 00 1c stw r31,28(r1)
1000007c: 7c 3f 0b 78 mr r31,r1
10000080: 39 20 00 05 li r9,5
10000084: 91 3f 00 08 stw r9,8(r31)
10000088: 81 3f 00 08 lwz r9,8(r31)
1000008c: 7d 3a f3 a6 mtspr 340,r9
10000090: 39 20 00 00 li r9,0
10000094: 7d 23 4b 78 mr r3,r9
10000098: 39 7f 00 20 addi r11,r31,32
1000009c: 83 eb ff fc lwz r31,-4(r11)
100000a0: 7d 61 5b 78 mr r1,r11
100000a4: 4e 80 00 20 blr
The "mtspr 340" part should be "mtspr 986" since the PowerPC 405 does not use
the PowerPC Book E SPRN register numbers.
Using -save-temps I see the following assembly
.file "filename.c"
.machine ppc
.section ".text"
.align 2
.globl main
.type main, @function
main:
stwu 1,-32(1)
stw 31,28(1)
mr 31,1
li 9,5
stw 9,8(31)
lwz 9,8(31)
#APP
# 4 "filename.c" 1
mttcr 9
# 0 "" 2
#NO_APP
li 9,0
mr 3,9
addi 11,31,32
lwz 31,-4(11)
mr 1,11
blr
.size main, .-main
.ident "GCC: (GNU) 6.1.0"
.section .note.GNU-stack,"",@progbits
Note the ".machine ppc" part which overrides the parameters provided at the as
command line. In this case using "gcc -v" I saw:
powerpc-softfloat-linux/bin/as -v -m405 -many -mbig -o filename.o filename.s
So instead of -m405 the assember uses the setting of -mppc. Per
https://sourceware.org/binutils/docs/as/PowerPC_002dOpts.html#PowerPC_002dOpts
this is PowerPC 603/604 assembly and not the requested PowerPC 403/405
assembly.
It appears this would happen for a number of the -m options, since the code in
rs6000.c has .machine ppc as the default if none of the powerN or ppc64
selections apply.
Searching the Internet for related info on this issue for PowerPC 4xx I did
find a related patch:
https://github.com/sba1/adtools/blob/master/gcc/5/patches/0003-Disable-.machine-directive-generation.patch
