debug/dwarf: support compressed debug sections #11773

qeedquan · 2015-07-18T01:55:53Z

I upgraded to go 1.5 beta2 and get this error when building any cgo libraries
cannot load DWARF output from $WORK/command-line-arguments/_obj//cgo.o: decoding dwarf section info at offset 0x0: too short

even simple programs that just does

package main

// #include <stdio.h>
import "C"

func main() {
    C.puts("test")
}

fails to build for me
Using gcc 4.9.2 on amd64

The text was updated successfully, but these errors were encountered:

alexbrainman · 2015-07-18T01:59:20Z

What does "go version" output?

Alex

ianlancetaylor · 2015-07-18T02:31:18Z

What operating system?

Can you show us the output of "go build -x" for a small failing program?

qeedquan · 2015-07-18T02:34:16Z

go version is "go1.5beta2 linux/amd64"

go build -x test.go (the program above):

WORK=/tmp/go-build438987599
mkdir -p $WORK/command-line-arguments/_obj/
cd /home/qeed
CGO_LDFLAGS="-g" "-O2" ./apps/go/pkg/tool/linux_amd64/cgo -objdir $WORK/command-line-arguments/_obj/ -importpath command-line-arguments -- -I $WORK/command-line-arguments/_obj/ test.go
# command-line-arguments
cannot load DWARF output from $WORK/command-line-arguments/_obj//_cgo_.o: decoding dwarf section info at offset 0x0: too short

ianlancetaylor · 2015-07-18T05:28:25Z

Thanks. Next step: copy test.go into an empty directory, cd to that directory, and run

CGO_LDFLAGS="-g -O2" go tool cgo -debug-gcc -objdir . -importpath command-line-arguments -- -I . test.go

Please attach the output of that.

Also, do you have GOROOT set in the environment?

qeedquan · 2015-07-18T06:51:06Z

I have GOROOT set, but I also tried to unset it and ran the program, either way it gives me an error
The cgo.o file: http://spark.ofloo.net/~qeed/_cgo_.o

$ gcc -E -dM -xc -m64 -I . - <<EOF
#line 3 "/home/qeed/t/test.go"
 #include <stdio.h>


#include <stddef.h> /* for ptrdiff_t and size_t below */

/* Define intgo when compiling with GCC.  */
typedef ptrdiff_t intgo;

typedef struct { char *p; intgo n; } _GoString_;
typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
_GoString_ GoString(char *p);
_GoString_ GoStringN(char *p, int l);
_GoBytes_ GoBytes(void *p, int n);
char *CString(_GoString_);
void *_CMalloc(size_t);
EOF
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#define FOPEN_MAX 16
#define _IO_STDIO 040000
#define __off_t_defined 
#define _IO_IS_APPENDING 0x1000
#define _GCC_SIZE_T 
#define __INO64_T_TYPE __UQUAD_TYPE
#define __UINT32_C(c) c ## U
#define __INTMAX_MAX__ 9223372036854775807L
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __size_t__ 
#define _IO_BUFSIZ _G_BUFSIZ
#define __FLT_DENORM_MIN__ 1.40129846432481707092e-45F
#define __BEGIN_NAMESPACE_C99 
#define __INT8_MAX__ 127
#define __UINT_FAST32_TYPE__ long unsigned int
#define __INO_T_MATCHES_INO64_T 1
#define _IO_fpos_t _G_fpos_t
#define __CHAR32_TYPE__ unsigned int
#define __FLT_MAX__ 3.40282346638528859812e+38F
#define __attribute_format_arg__(x) __attribute__ ((__format_arg__ (x)))
#define __INT32_TYPE__ int
#define __SIZEOF_DOUBLE__ 8
#define __FLT_MIN_10_EXP__ (-37)
#define _IO_BE(expr,res) __builtin_expect ((expr), res)
#define __SWORD_TYPE long int
#define __INTMAX_TYPE__ long int
#define __DEC128_MAX_EXP__ 6145
#define _T_SIZE 
#define __va_arg_pack() __builtin_va_arg_pack ()
#define __ATOMIC_CONSUME 1
#define _IO_stdout ((_IO_FILE*)(&_IO_2_1_stdout_))
#define __GNUC_MINOR__ 9
#define __UINTMAX_MAX__ 18446744073709551615UL
#define __DEC32_MANT_DIG__ 7
#define __DBL_MAX_10_EXP__ 308
#define __FILE_defined 1
#define __LDBL_DENORM_MIN__ 3.64519953188247460253e-4951L
#define __INT16_C(c) c
#define __U32_TYPE unsigned int
#define __STDC__ 1
#define __attribute_malloc__ __attribute__ ((__malloc__))
#define __PTRDIFF_TYPE__ long int
#define __attribute_noinline__ __attribute__ ((__noinline__))
#define _IO_HEX 0100
#define __ATOMIC_SEQ_CST 5
#define __CLOCK_T_TYPE __SYSCALL_SLONG_TYPE
#define _IO_fpos64_t _G_fpos64_t
#define __UINT32_TYPE__ unsigned int
#define __UINTPTR_TYPE__ long unsigned int
#define __DEC64_SUBNORMAL_MIN__ 0.000000000000001E-383DD
#define __FSFILCNT64_T_TYPE __UQUAD_TYPE
#define __DEC128_MANT_DIG__ 34
#define __LDBL_MIN_10_EXP__ (-4931)
#define __attribute_deprecated__ __attribute__ ((__deprecated__))
#define _IO_wint_t wint_t
#define __SIZEOF_LONG_LONG__ 8
#define __USE_ATFILE 1
#define _GCC_PTRDIFF_T 
#define __GCC_ATOMIC_LLONG_LOCK_FREE 2
#define __LDBL_DIG__ 18
#define __FLT_DECIMAL_DIG__ 9
#define __UINT_FAST16_MAX__ 18446744073709551615UL
#define __GNUC_GNU_INLINE__ 1
#define ___int_ptrdiff_t_h 
#define __GCC_ATOMIC_SHORT_LOCK_FREE 2
#define _IO_ftrylockfile(_fp) 
#define __glibc_likely(cond) __builtin_expect ((cond), 1)
#define __UINT_FAST8_TYPE__ unsigned char
#define __P(args) args
#define __ATOMIC_ACQ_REL 4
#define __WCHAR_T 
#define __ATOMIC_RELEASE 3
#define _IO_peekc(_fp) _IO_peekc_unlocked (_fp)
$ gcc -w -Wno-error -o./_cgo_.o -gdwarf-2 -c -xc -I . -m64 - <<EOF
#line 3 "/home/qeed/t/test.go"
 #include <stdio.h>


#include <stddef.h> /* for ptrdiff_t and size_t below */

/* Define intgo when compiling with GCC.  */
typedef ptrdiff_t intgo;

typedef struct { char *p; intgo n; } _GoString_;
typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
_GoString_ GoString(char *p);
_GoString_ GoStringN(char *p, int l);
_GoBytes_ GoBytes(void *p, int n);
char *CString(_GoString_);
void *_CMalloc(size_t);
#line 1 "not-declared"
void __cgo_f_1_1(void) { __typeof__(puts) *__cgo_undefined__; }
#line 1 "not-type"
void __cgo_f_1_2(void) { puts *__cgo_undefined__; }
#line 1 "not-const"
void __cgo_f_1_3(void) { enum { __cgo__undefined__ = (puts)*1 }; }
#line 1 "completed"
int __cgo__1 = __cgo__2;
EOF
not-type: In function '__cgo_f_1_2':
not-type:1:32: error: '__cgo_undefined__' undeclared (first use in this function)
not-type:1:32: note: each undeclared identifier is reported only once for each function it appears in
not-const: In function '__cgo_f_1_3':
not-const:1:60: error: invalid operands to binary * (have 'int (*)(const char *)' and 'int')
completed: At top level:
completed:1:16: error: '__cgo__2' undeclared here (not in a function)
$ gcc -w -Wno-error -o./_cgo_.o -gdwarf-2 -c -xc -I . -m64 - <<EOF
#line 3 "/home/qeed/t/test.go"
 #include <stdio.h>


#include <stddef.h> /* for ptrdiff_t and size_t below */

/* Define intgo when compiling with GCC.  */
typedef ptrdiff_t intgo;

typedef struct { char *p; intgo n; } _GoString_;
typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
_GoString_ GoString(char *p);
_GoString_ GoStringN(char *p, int l);
_GoBytes_ GoBytes(void *p, int n);
char *CString(_GoString_);
void *_CMalloc(size_t);
__typeof__(puts) *__cgo__0;
__typeof__(puts) *__cgo__1;
long long __cgodebug_data[] = {
    0,
    0,
    1
};
EOF
cannot load DWARF output from ./_cgo_.o: decoding dwarf section info at offset 0x0: too short

ianlancetaylor · 2015-07-18T17:58:27Z

You should never set GOROOT in the environment, but I understand that you are saying that this is not the problem here.

Please put this (from the end of the above) into a file x.c:

#line 3 "/home/qeed/t/test.go"
#include <stdio.h>

#include <stddef.h> /* for ptrdiff_t and size_t below */

/* Define intgo when compiling with GCC. */
typedef ptrdiff_t intgo;

typedef struct { char *p; intgo n; } GoString;
typedef struct { char *p; intgo n; intgo c; } GoBytes;
GoString GoString(char *p);
GoString GoStringN(char *p, int l);
GoBytes GoBytes(void *p, int n);
char *CString(GoString);
void *_CMalloc(size_t);
typeof(puts) *cgo__0;
__typeof(puts) *__cgo__1;
long long __cgodebug_data[] = {
0,
0,
1
};

Then run

gcc -w -Wno-error -o./cgo.o -gdwarf-2 -c -xc -I . -m64 x.c

Then attach the output of

readelf -s --wide ./cgo.o

Thanks.

qeedquan · 2015-07-18T18:47:21Z

I should also say that 1.5beta1 used to work, so there was a commit between then and now that broke it

Symbol table '.symtab' contains 15 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FILE LOCAL DEFAULT ABS x.c
2: 0000000000000000 0 SECTION LOCAL DEFAULT 1
3: 0000000000000000 0 SECTION LOCAL DEFAULT 2
4: 0000000000000000 0 SECTION LOCAL DEFAULT 3
5: 0000000000000000 0 SECTION LOCAL DEFAULT 4
6: 0000000000000000 0 SECTION LOCAL DEFAULT 6
7: 0000000000000000 0 SECTION LOCAL DEFAULT 7
8: 0000000000000000 0 SECTION LOCAL DEFAULT 9
9: 0000000000000000 0 SECTION LOCAL DEFAULT 10
10: 0000000000000000 0 SECTION LOCAL DEFAULT 12
11: 0000000000000000 0 SECTION LOCAL DEFAULT 11
12: 0000000000000008 8 OBJECT GLOBAL DEFAULT COM __cgo__0
13: 0000000000000008 8 OBJECT GLOBAL DEFAULT COM __cgo__1
14: 0000000000000000 24 OBJECT GLOBAL DEFAULT 2 __cgodebug_data

ianlancetaylor · 2015-07-18T20:05:33Z

My apologies, I wrote the wrong thing. I was looking for

readelf -S --wide ./_cgo.o

(upper case -S, not lower case -s).

It's extremely odd that this changed between beta1 and beta2. I can not see any relevant changes in cmd/cgo, cmd/go, debug/elf, debug/dwarf, and I can't think of any other relevant code.

qeedquan · 2015-07-18T20:19:37Z

Hm, I have tried reverting back to 1.4.2 and now it gives me the same error, maybe there is something wrong with my gcc install, though I can't think of anything I did recently that could affect it. I tried with CC=clang and it works for me.

I might have to reinstall some packages, but in the mean time let me paste the readelf output
readelf -S --wide ./cgo.o

There are 16 section headers, starting at offset 0x668:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .text             PROGBITS        0000000000000000 000040 000000 00  AX  0   0  1
  [ 2] .data             PROGBITS        0000000000000000 000040 000018 00  WA  0   0 16
  [ 3] .bss              NOBITS          0000000000000000 000058 000000 00  WA  0   0  1
  [ 4] .zdebug_info      PROGBITS        0000000000000000 000058 00007e 00      0   0  1
  [ 5] .rela.zdebug_info RELA            0000000000000000 0003d8 0001e0 18   I 14   4  8
  [ 6] .zdebug_abbrev    PROGBITS        0000000000000000 0000d6 000069 00      0   0  1
  [ 7] .zdebug_aranges   PROGBITS        0000000000000000 00013f 00001f 00      0   0  1
  [ 8] .rela.zdebug_aranges RELA            0000000000000000 0005b8 000018 18   I 14   7  8
  [ 9] .debug_line       PROGBITS        0000000000000000 00015e 000035 00      0   0  1
  [10] .zdebug_str       PROGBITS        0000000000000000 000193 0000a0 01  MS  0   0  1
  [11] .comment          PROGBITS        0000000000000000 000233 000012 01  MS  0   0  1
  [12] .note.GNU-stack   PROGBITS        0000000000000000 000245 000000 00      0   0  1
  [13] .shstrtab         STRTAB          0000000000000000 0005d0 000093 00      0   0  1
  [14] .symtab           SYMTAB          0000000000000000 000248 000168 18     15  12  8
  [15] .strtab           STRTAB          0000000000000000 0003b0 000027 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
  I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)

ianlancetaylor · 2015-07-18T20:33:44Z

Thanks. Your compiler is emitting compressed debug info. The Go packages don't know how to parse that yet. This is done by the assembler, via the --compress-debug-sections option. Something must have changed to cause that to happen by default.

rsc · 2015-11-05T02:06:10Z

/cc @aclements

aclements · 2015-12-02T03:34:32Z

@ianlancetaylor, is there a reference for compressed DWARF? The best I was able to find is a few sentences at https://sourceware.org/gdb/wiki/Internals%20Debugging-File-Formats (which may be sufficient).

I presume the relocations must apply to the decompressed sections, even though the section table technically says they apply to the compressed sections? In that case, I think we have to do this in debug/elf before passing the sections to debug/dwarf, simply because debug/elf handles the relocations.

ianlancetaylor · 2015-12-02T04:34:32Z

That link is the old way. The new way is the SHF_COMPRESSED flag in an ELF section. Search for SHF_COMPRESSED in http://www.sco.com/developers/gabi/latest/ch4.sheader.html .

As you say, relocation offsets apply to the uncompressed data.

gopherbot · 2015-12-02T05:00:51Z

CL https://golang.org/cl/17340 mentions this issue.

aclements · 2015-12-02T15:15:21Z

That link is the old way. The new way is the SHF_COMPRESSED flag in an ELF section. Search for SHF_COMPRESSED in http://www.sco.com/developers/gabi/latest/ch4.sheader.html .

Okay. Is there a flag to ask gcc 4.8.4/as 2.24/ld 2.24 (gold 1.11?) to generate compressed sections so I can test my implementation? Or do I need a newer toolchain?

ianlancetaylor · 2015-12-02T17:26:41Z

Looks like you need a newer toolchain. In fact, it looks like you need 2.26, which doesn't exist yet. I can send you an object if you like.

aclements · 2015-12-02T17:29:22Z

In fact, it looks like you need 2.26, which doesn't exist yet.

Oh. :)

I can send you an object if you like.

Please do. Both ELF32 and ELF64 if that's possible.

ianlancetaylor · 2015-12-02T17:36:30Z

Please do. Both ELF32 and ELF64 if that's possible.

Sent by direct e-mail.

gopherbot · 2015-12-02T18:00:49Z

CL https://golang.org/cl/17341 mentions this issue.

GCC and LLVM support zlib-compressing DWARF debug sections (and there's some evidence that this may be happening by default in some circumstances now). Add support for reading compressed DWARF sections. Since ELF relocations apply to the decompressed data, decompression is done before applying relocations. Since relcations are applied by debug/elf, decompression must also be handled there. Note that this is different from compressed ELF sections, which is a more general mechanism used by very recent versions of GCC. Updates #11773. Change-Id: I3f4bf1b04d0802cc1e8fcb7c2a5fcf6c467c5089 Reviewed-on: https://go-review.googlesource.com/17340 Reviewed-by: Ian Lance Taylor <[email protected]> Run-TryBot: Austin Clements <[email protected]> TryBot-Result: Gobot Gobot <[email protected]> Reviewed-by: Russ Cox <[email protected]>

qeedquan changed the title ~~go 1.5beta2 fails to work with gcc 4.9.2~~ go 1.5beta2 cgo fails to work with gcc 4.9.2 Jul 18, 2015

ianlancetaylor added this to the Go1.5 milestone Jul 18, 2015

ianlancetaylor changed the title ~~go 1.5beta2 cgo fails to work with gcc 4.9.2~~ cmd/cgo: go 1.5beta2 cgo fails to work with gcc 4.9.2 Jul 18, 2015

ianlancetaylor changed the title ~~cmd/cgo: go 1.5beta2 cgo fails to work with gcc 4.9.2~~ debug/dwarf: support compressed debug sections Jul 18, 2015

ianlancetaylor modified the milestones: Go1.6, Go1.5 Jul 18, 2015

josharian mentioned this issue Jul 20, 2015

cmd/link: compress debug info #11799

Closed

aclements closed this as completed in 7648387 Dec 3, 2015

vbatts mentioned this issue Aug 18, 2016

development/google-go-lang: Updated for version go1.7 willysr/slackbuilds#6

Closed

golang locked and limited conversation to collaborators Dec 14, 2016

gopherbot added the FrozenDueToAge label Dec 14, 2016

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debug/dwarf: support compressed debug sections #11773

debug/dwarf: support compressed debug sections #11773

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debug/dwarf: support compressed debug sections #11773

debug/dwarf: support compressed debug sections #11773

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