debug/dwarf: support compressed debug sections

[qeedquan]

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

[alexbrainman]

What does "go version" output?

Alex

[ianlancetaylor]

What operating system?

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

[qeedquan]

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]

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]

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 __SIZE_T 
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#define __WINT_MIN__ 0U
#define __linux__ 1
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#define __KERNEL_STRICT_NAMES 
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#define __USER_LABEL_PREFIX__ 
#define __GLIBC__ 2
#define __END_DECLS 
#define __CONCAT(x,y) x ## y
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#define __LDBL_HAS_INFINITY__ 1
#define __SLONG32_TYPE int
#define _IO_LINE_BUF 0x200
#define _IOS_NOCREATE 32
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#define TMP_MAX 238328
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#define __DEC32_MIN_EXP__ (-94)
#define __DADDR_T_TYPE __S32_TYPE
#define __END_NAMESPACE_C99 
#define __FD_SETSIZE 1024
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#define __PTRDIFF_T 
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#define _IO_IS_FILEBUF 0x2000
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#define _BSD_PTRDIFF_T_ 
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#define _VA_LIST_DEFINED 
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#define _IO_size_t size_t
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#define __stub_lchmod 
#define __DEC64_MANT_DIG__ 16
#define __INT64_MAX__ 9223372036854775807L
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#define __INTPTR_MAX__ 9223372036854775807L
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#define ____FILE_defined 1
#define _IOLBF 1
#define _IO_UPPERCASE 01000
#define __SSE2__ 1
#define __KEY_T_TYPE __S32_TYPE
#define __WORDSIZE 64
#define __BEGIN_DECLS 
#define __LDBL_MANT_DIG__ 64
#define __DBL_HAS_QUIET_NAN__ 1
#define _IO_BAD_SEEN 0x4000
#define __GNUC_VA_LIST 
#define __SIG_ATOMIC_MIN__ (-__SIG_ATOMIC_MAX__ - 1)
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#define __RLIM_T_TYPE __SYSCALL_ULONG_TYPE
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#define __INTPTR_TYPE__ long int
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#define __HAVE_COLUMN 
#define __stub_fdetach 
#define __UINTPTR_MAX__ 18446744073709551615UL
#define __DEC64_MIN_EXP__ (-382)
#define __stub_chflags 
#define putc(_ch,_fp) _IO_putc (_ch, _fp)
#define __UQUAD_TYPE unsigned long int
#define __USE_POSIX 1
#define __INT_FAST64_MAX__ 9223372036854775807L
#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
#define BUFSIZ _IO_BUFSIZ
#define __FLT_DIG__ 6
#define __FSID_T_TYPE struct { int __val[2]; }
#define _WCHAR_T_DECLARED 
#define __UINT_FAST64_TYPE__ long unsigned int
#define _IO_putc_unlocked(_ch,_fp) (_IO_BE ((_fp)->_IO_write_ptr >= (_fp)->_IO_write_end, 0) ? __overflow (_fp, (unsigned char) (_ch)) : (unsigned char) (*(_fp)->_IO_write_ptr++ = (_ch)))
#define __LDBL_REDIR_DECL(name) 
#define __INT_MAX__ 2147483647
#define __amd64__ 1
#define __S16_TYPE short int
#define __bos(ptr) __builtin_object_size (ptr, __USE_FORTIFY_LEVEL > 1)
#define _T_SIZE_ 
#define _G_va_list __gnuc_va_list
#define _IOS_INPUT 1
#define __INT64_TYPE__ long int
#define __FLT_MAX_EXP__ 128
#define __ORDER_BIG_ENDIAN__ 4321
#define __ptr_t void *
#define __DBL_MANT_DIG__ 53
#define ___int_size_t_h 
#define __TIMER_T_TYPE void *
#define __INT_LEAST64_MAX__ 9223372036854775807L
#define __GCC_ATOMIC_CHAR16_T_LOCK_FREE 2
#define __GLIBC_MINOR__ 21
#define __DEC64_MIN__ 1E-383DD
#define __WINT_TYPE__ unsigned int
#define __UINT_LEAST32_TYPE__ unsigned int
#define __SIZEOF_SHORT__ 2
#define __SSE__ 1
#define __LDBL_MIN_EXP__ (-16381)
#define _IO_va_list __gnuc_va_list
#define stdout stdout
#define __REDIRECT_NTHNL(name,proto,alias) name proto __asm__ (__ASMNAME (#alias)) __THROWNL
#define EOF (-1)
#define __INT_LEAST8_MAX__ 127
#define __extern_inline extern __inline
#define __USE_POSIX199309 1
#define ____mbstate_t_defined 1
#define __SIZEOF_INT128__ 16
#define __BLKCNT64_T_TYPE __SQUAD_TYPE
#define __LDBL_MAX_10_EXP__ 4932
#define __ATOMIC_RELAXED 0
#define __FSBLKCNT_T_TYPE __SYSCALL_ULONG_TYPE
#define __DBL_EPSILON__ ((double)2.22044604925031308085e-16L)
#define __stub_stty 
#define _SIZET_ 
#define _LP64 1
#define __REDIRECT_NTH_LDBL(name,proto,alias) __REDIRECT_NTH (name, proto, alias)
#define __UINT8_C(c) c
#define __INT_LEAST32_TYPE__ int
#define __wchar_t__ 
#define SEEK_END 2
#define __SIZEOF_WCHAR_T__ 4
#define __USE_POSIX_IMPLICITLY 1
#define __UINT64_TYPE__ long unsigned int
#define __REDIRECT_NTH(name,proto,alias) name proto __asm__ (__ASMNAME (#alias)) __THROW
#define _IO_RIGHT 04
#define __END_NAMESPACE_STD 
#define _STDDEF_H_ 
#define __INT_FAST8_TYPE__ signed char
#define __PID_T_TYPE __S32_TYPE
#define P_tmpdir "/tmp"
#define __attribute_pure__ __attribute__ ((__pure__))
#define __WORDSIZE_TIME64_COMPAT32 1
#define _IO_stdin ((_IO_FILE*)(&_IO_2_1_stdin_))
#define _IO_cleanup_region_start(_fct,_fp) 
#define _IO_NO_READS 4
#define _IO_DEC 020
#define __DBL_DECIMAL_DIG__ 17
#define __FXSR__ 1
#define __DEC_EVAL_METHOD__ 2
#define _SIZE_T 
#define _IO_ERR_SEEN 0x20
#define __ULONG32_TYPE unsigned int
#define _G_config_h 1
#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]

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]

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]

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]

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]

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.