Hi, Alexi
Thank you for your guidence, and by referencing your last mail
and other llvm backends, I found setting
BPFMCAsmInfo::SupportsDebugInformation = true in BPFMCAsmInfo.h
and fix some unhandeled switch can make llc output debug_info,
but important information is missing in the result:
bpf:
<1><2a>: Abbrev Number: 2 (DW_TAG_subprogram)
<2b> DW_AT_low_pc : 0x0
<33> DW_AT_high_pc : 0x60
<37> Unknown AT value: 3fe7: 1
<37> DW_AT_frame_base : 1 byte block: 5a (DW_OP_reg10 (r10))
<39> DW_AT_name : (indirect string, offset: 0x0): clang
version 3.7.0 (http://llvm.org/git/clang.git..
<3d> DW_AT_decl_file : 1
<3e> DW_AT_decl_line : 3
<3f> DW_AT_prototyped : 1
<3f> DW_AT_type : <0x65>
<43> DW_AT_external : 1
<43> Unknown AT value: 3fe1: 1
<2><43>: Abbrev Number: 3 (DW_TAG_formal_parameter)
<44> DW_AT_name : (indirect string, offset: 0x0): clang
version 3.7.0 (http://llvm.org/git/clang.git..
<48> DW_AT_decl_file : 1
<49> DW_AT_decl_line : 3
<4a> DW_AT_type : <0x65>
Compares to x86 platform result:
<1><26>: Abbrev Number: 2 (DW_TAG_subprogram)
<27> DW_AT_low_pc : 0x0
<2b> DW_AT_high_pc : 0x16
<2f> Unknown AT value: 3fe7: 1
<2f> DW_AT_frame_base : 1 byte block: 54 (DW_OP_reg4 (esp))
<31> DW_AT_name : (indirect string, offset: 0xcf): testprog
<35> DW_AT_decl_file : 1
<36> DW_AT_decl_line : 3
<37> DW_AT_prototyped : 1
<37> DW_AT_type : <0x65>
<3b> DW_AT_external : 1
<3b> Unknown AT value: 3fe1: 1
<2><3b>: Abbrev Number: 3 (DW_TAG_formal_parameter)
<3c> DW_AT_location : 2 byte block: 91 4 (DW_OP_fbreg: 4)
<3f> DW_AT_name : (indirect string, offset: 0xdc): myvar_a
<43> DW_AT_decl_file : 1
<44> DW_AT_decl_line : 3
<45> DW_AT_type : <0x65>
The bpf result lacks of DW_AT_location, and DW_AT_name gives no
infomation.
Then I used 'llc print-after*' command to check each pass and
wanted to find by which step the debug infomation is dropped,
things looks similar until the passes between 'verify' and
'expand-isel-pseudos':
x86:
$ llc -march=x86 --print-before-all -print-after-all
-stop-after=expand-isel-pseudos test.ll
# *** IR Dump Before Expand ISel Pseudo-instructions ***:
# Machine code for function testprog: SSA
Frame Objects:
fi#-2: size=4, align=4, fixed, at location [SP+8]
fi#-1: size=4, align=16, fixed, at location [SP+4]
BB#0: derived from LLVM BB %entry
DBG_VALUE <fi#-1>, 0, !"myvar_a", <!15>; line no:3
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
DBG_VALUE <fi#-2>, 0, !"myvar_b", <!15>; line no:3
%vreg0<def> = MOV32rm <fi#-2>, 1, %noreg, 0, %noreg; mem:LD4[FixedStack-2]
; GR32:%vreg0
bpf:
$ llc -march=bpf --print-before-all -print-after-all
-stop-after=expand-isel-pseudos test.ll
# *** IR Dump Before Expand ISel Pseudo-instructions ***:
# Machine code for function testprog: SSA
Function Live Ins: %R1 in %vreg0, %R2 in %vreg1
BB#0: derived from LLVM BB %entry
Live Ins: %R1 %R2
%vreg1<def> = COPY %R2; GPR:%vreg1
%vreg0<def> = COPY %R1; GPR:%vreg0
%vreg2<def> = LD_imm64 2147483648; GPR:%vreg2
I think maybe this missing 'DBG_VALUE' causes the problem, but
I'm stuck here and hope you can give more advice.
Thank you!
On 2015/7/17 12:27, Alexei Starovoitov wrote:
clang -O2 -emit-llvm -g a.c -S -o a.ll
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