On Mon, Feb 25, 2019 at 12:51 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Mon, Feb 25, 2019 at 12:08 PM Arnaldo Carvalho de Melo
> <arnaldo.melo@xxxxxxxxx> wrote:
> >
> > Em Mon, Feb 25, 2019 at 11:42:29AM -0800, Andrii Nakryiko escreveu:
> > > On Mon, Feb 25, 2019 at 11:00 AM Arnaldo Carvalho de Melo> <arnaldo.melo@xxxxxxxxx> wrote:
> >
> > > > Em Mon, Feb 25, 2019 at 01:02:39PM -0300, Arnaldo Carvalho de Melo escreveu:
> > > > > So yeah, the BTF encoder/decoder is working just fine, the problem is in
> > > > > pahole's DWARF code, lemme see...
> > > >
> > > > Please try the patch below, for me btfdiff continues to show no diff for
> > > > all types in my vmlinux and now it also produces the same output for
> > > > when the first element of a bitfield has its bit_size equal to its
> > > > byte_size * 8:
> > >
> > > Yes, this fixes all the issues I've seen. btfdiff output is now empty
> > > for my kernel image. Thanks for quick fix!
> > >
> > > Reviewed-by: Andrii Nakryiko <andriin@xxxxxx>
> >
> > Thanks, just for some extra testing I tried encoding BTF for glibc 2.28:
> >
> > [acme@quaco pahole]$ pahole -JV libc-2.28.so.debug
> > <BIG snip>
>
> <snip>
>
> > [386075] INT long unsigned int size=8 bit_offset=0 nr_bits=64 encoding=(none)
> > Cannot open libc-2.28.so.debug
> > Failed to encode BTF
>
> I've tried the same on libc-2.26.so.debug and it worked.
>
> It failes after BTF encoding and deduping is done, exactly when it
> tries to re-open libc-2.28.so.debug to write out new contents. Not
> sure why it would fail, as it seems to be just plain open() call, but
> the fact that we both can repro this means there is something there.
>
> It also seems that libc-2.28.so.debug is corrupted:
>
> $ readelf -n /home/andriin/local/btf/libc-2.26.so.debug | grep
> 'Unknown note type' | wc -l
> 0
> $ readelf -n /home/andriin/local/btf/libc-2.28.so.debug | grep
> 'Unknown note type' | wc -l
> 17953
>
Ignore everything I've said (though 'Unknown note type' issue is
strange), for me it was just permissions issues.
$ chmod +rw /home/andriin/local/btf/libc-2.28.so.debug
$ ~/local/pahole/build/pahole -J ~/local/btf/libc-2.28.so.debug
$ PAHOLE=~/local/pahole/build/pahole ./btfdiff ~/local/btf/libc-2.28.so.debug
base_type__name_to_size: base_type _Float128
class__fixup_btf_bitfields: unknown base type name "_Float128"!
base_type__name_to_size: base_type _Float128
class__fixup_btf_bitfields: unknown base type name "_Float128"!
base_type__name_to_size: base_type _Float128
class__fixup_btf_bitfields: unknown base type name "_Float128"!
base_type__name_to_size: base_type _Float128
class__fixup_btf_bitfields: unknown base type name "_Float128"!
base_type__name_to_size: base_type _Float128
class__fixup_btf_bitfields: unknown base type name "_Float128"!
base_type__name_to_size: base_type _Float128
class__fixup_btf_bitfields: unknown base type name "_Float128"!
--- /tmp/btfdiff.dwarf.aV4wSL 2019-02-25 13:31:54.787923673 -0800
+++ /tmp/btfdiff.btf.22NQmJ 2019-02-25 13:31:54.802923668 -0800
@@ -461,9 +461,15 @@ struct La_x86_64_retval {
uint64_t lrv_rdx; /* 8 8 */
La_x86_64_xmm lrv_xmm0; /* 16 16 */
La_x86_64_xmm lrv_xmm1; /* 32 16 */
- long double lrv_st0; /* 48 16 */
+ long double lrv_st0; /* 48 8 */
+
+ /* XXX 8 bytes hole, try to pack */
+
/* --- cacheline 1 boundary (64 bytes) --- */
- long double lrv_st1; /* 64 16 */
+ long double lrv_st1; /* 64 8 */
+
+ /* XXX 8 bytes hole, try to pack */
+
La_x86_64_vector lrv_vector0; /* 80 64 */
/* --- cacheline 2 boundary (128 bytes) was 16 bytes ago --- */
La_x86_64_vector lrv_vector1; /* 144 64 */
@@ -472,6 +478,7 @@ struct La_x86_64_retval {
__int128 lrv_bnd1; /* 224 16 */
/* size: 240, cachelines: 4, members: 10 */
+ /* sum members: 224, holes: 2, sum holes: 16 */
/* last cacheline: 48 bytes */
};
struct r_debug {
@@ -2044,7 +2051,7 @@ union ieee754_float {
} ieee_nan; /* 0 4 */
};
union ieee854_long_double {
- long double d; /* 0 16 */
+ long double d; /* 0 8 */
struct {
unsigned int mantissa1:32; /* 0: 0 4 */
unsigned int mantissa0:32; /* 4: 0 4 */
@@ -2141,7 +2148,7 @@ struct ucontext_t {
/* last cacheline: 8 bytes */
};
union ieee854_float128 {
- _Float128 d; /* 0 16 */
+ _Float128 d; /* 0 0 */
struct {
unsigned int mantissa3:32; /* 0: 0 4 */
unsigned int mantissa2:32; /* 4: 0 4 */
@@ -2219,7 +2226,7 @@ union printf_arg {
long unsigned int pa_u_long_int; /* 0 8 */
long long unsigned int pa_u_long_long_int; /* 0 8 */
double pa_double; /* 0 8 */
- long double pa_long_double; /* 0 16 */
+ long double pa_long_double; /* 0 8 */
const char * pa_string; /* 0 8 */
const wchar_t * pa_wstring; /* 0 8 */
void * pa_pointer; /* 0 8 */
Seems like "long double" size is invalid for BTF. And we should
probably add "_Float128" as another "well known" base type name?
Though for the latter, it probably would be better to resolve base
type size using BTF data itself.
> > [acme@quaco pahole]$
