[llvm-bugs] [Bug 34715] New: compiler-rt builtins are broken for thumb

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34715

            Bug ID: 34715
           Summary: compiler-rt builtins are broken for thumb
           Product: compiler-rt
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: compiler-rt
          Assignee: unassignedbugs at nondot.org
          Reporter: manojgupta at google.com
                CC: compnerd at compnerd.org, efriedma at codeaurora.org,
                    llozano at chromium.org, llvm-bugs at lists.llvm.org,
                    peter.smith at linaro.org, pirama at google.com,
                    srhines at google.com, weimingz at codeaurora.org

Many Compiler-rt ARM asm builtins are missing .thumb declaration. As a result,
they are compiled in ARM mode.

r310884 forced function declaration to be thumb when the thumb state is
supported.
This created a mismatch in generated code where the encoding is done in ARM
mode but function is marked as a thumb function.

#define DEFINE_COMPILERRT_FUNCTION(name)                                      
\
   FILE_LEVEL_DIRECTIVE SEPARATOR                                              
\
    .globl SYMBOL_NAME(name) SEPARATOR                                         
 \
    SYMBOL_IS_FUNC(SYMBOL_NAME(name)) SEPARATOR                                
 \
    DECLARE_SYMBOL_VISIBILITY(name)                                            
 \
 +  DECLARE_FUNC_ENCODING      // This forces function to be declared as a
thumb function                                                  \
    SYMBOL_NAME(name):

e.g.

$ clang -Qunused-arguments -pie -mthumb -DVISIBILITY_HIDDEN -O2 -pipe
-rtlib=libgcc -fomit-frame-pointer -mfpu=vfpv3 -march=armv7-a -mfloat-abi=hard
-fno-lto -std=c11 -fPIC -fno-builtin -fvisibility=hidden
-DCOMPILER_RT_ARMHF_TARGET -o adddf3vfp.S.o -c 
work/compiler-rt/lib/builtins/arm/adddf3vfp.S -target
armv7a-cros-linux-gnueabihf -mfloat-abi=hard

$ arm-linux-gnueabihf-objdump -d adddf3vfp.S.o

Disassembly of section .text:

00000000 <__adddf3vfp>:
   0:   ee300b01        vadd.f64        d0, d0, d1 // These are ARM
instructions, not thumb/thumb2
   4:   e12fff1e        bx      lr

$ readelf -s adddf3vfp.S.o

Previous: 
Symbol table '.symtab' contains 3 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 00000000     0 NOTYPE  LOCAL  DEFAULT    2 $a.0
     2: 00000000     8 FUNC    GLOBAL HIDDEN     2 __adddf3vfp

After r310884:
Symbol table '.symtab' contains 3 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 00000000     0 NOTYPE  LOCAL  DEFAULT    2 $a.0
     2: 00000001     8 FUNC    GLOBAL HIDDEN     2 __adddf3vfp // Note the
difference in the field Value

Because of this, linker think __adddf3vfp is a thumb function but the encoding
uses arm format.

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