ARM JIT should support ARMCompilationCallback in thumb2

[nlewycky]

Bugzilla Link	6065
Resolution	DUPLICATE
Resolved on	Feb 02, 2011 03:17
Version	trunk
OS	Linux
CC	@asl

Extended Description

This inline-asm in ARMJITInfo.cpp's ARMCompilationCallback:

// Return to the (newly modified) stub to invoke the real function.
// The above twiddling of the saved return addresses allows us to
// deallocate everything, including the LR the stub saved, all in one
// pop instruction.
"ldmia  sp!, {r0, r1, r2, r3, lr, pc}\n"

does not assemble as thumb2:

llvm[3]: Compiling ARMJITInfo.cpp for Release-Asserts build
/tmp/ccWGkQ6d.s: Assembler messages:
/tmp/ccWGkQ6d.s:28: Error: LR and PC should not both be in register list -- `ldmia sp!,{r0,r1,r2,r3,lr,pc}'
make[3]: *** [/home/nlewycky/llvm/lib/Target/ARM/Release-Asserts/ARMJITInfo.o] Error 1

with '-Os -mthumb' flags to gcc instead of -O2.

[llvmbot]

Based on the definition of LDMIA in the ARM architecture reference manual,

ldmia is define as below.

if W == 1' && Rn == 1101' then SEE POP;
n = UInt(Rn); registers = P:M:'0':register_list; wback = (W == 1'); if n == 15 || BitCount(registers) < 2 || (P == 1' && M == 1') then UNPREDICTABLE; if registers<15> == 1' && InITBlock() && !LastInITBlock() then UNPREDICTABLE;
if wback && registers == `1' then UNPREDICTABLE;

Note that if both P and M is '1', the result is UNPREDICTABLE. In the inlined assembly below, both lr and pc are to be accessed. So it's not a valid assembly code.

This inline-asm in ARMJITInfo.cpp's ARMCompilationCallback:

// Return to the (newly modified) stub to invoke the real function.
// The above twiddling of the saved return addresses allows us to
// deallocate everything, including the LR the stub saved, all in one
// pop instruction.
"ldmia  sp!, {r0, r1, r2, r3, lr, pc}\n"

does not assemble as thumb2:

llvm[3]: Compiling ARMJITInfo.cpp for Release-Asserts build
/tmp/ccWGkQ6d.s: Assembler messages:
/tmp/ccWGkQ6d.s:28: Error: LR and PC should not both be in register list --
`ldmia sp!,{r0,r1,r2,r3,lr,pc}'
make[3]: *** [/home/nlewycky/llvm/lib/Target/ARM/Release-Asserts/ARMJITInfo.o]
Error 1

with '-Os -mthumb' flags to gcc instead of -O2.

[llvmbot]

Right -- my other mistake is that I was building in thumb1 instead of thumb2. I'll try thumb2 tomorrow but I don't really expect it to work any better than a build with thumb did.

[llvmbot]

Indeed, in thumb2 mode (passing -mthumb -mcpu=cortex-a8) I get the same assembler error.

[llvmbot]

I'm new to LLVM. At least in GCC, -mthumb can mean both T1 and T2; It depends on which cpu you select.
For example:
-mthumb -mcpu=cortex-a8: T2
-mthumb -mcpu=arm1156t2-s: T2
-mthumb -march=armv7-a: T2
-mthumb -march=armv6t2: T2

-mthumb -mcpu=arm926ej-s: T1
-mthumb -mcpu=arm1136jf-s: T1
-mthumb -march=armv5: T1
-mthumb -march=armv6: T1

[llvmbot]

patch, make two pops when thumb are defined.
Would making two pops for thumb instead of one big one solve this issue?

[llvmbot]

fixed in svn r124694

*** This bug has been marked as a duplicate of bug llvm/llvm-bugzilla-archive#9081 ***

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#9081