| Message ID | 20210111151146.27850-1-szabolcs.nagy@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | elf: work around a gcc bug in elf_get_dynamic_info | expand |
On 11/01/2021 12:11, Szabolcs Nagy via Libc-alpha wrote: > Since commit 2f056e8a5dd4dc0f075413f931e82cede37d1057 > "aarch64: define PI_STATIC_AND_HIDDEN", > building glibc with gcc-8 on aarch64 fails with > > /BLD/elf/librtld.os: in function `elf_get_dynamic_info': > /SRC/elf/get-dynamic-info.h:70:(.text+0xad8): relocation truncated to > fit: R_AARCH64_ADR_PREL_PG_HI21 against symbol `_rtld_local' defined > in .data section in /BLD/elf/librtld.os > > This is a gcc bug: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98618 > > Rewriting the affected code in elf_get_dynamic_info > seems to make this issue go away on old gcc. > > The change makes the logic a bit clearer too (by > separating the index computation and array update) > and drops an older gcc workaround (since gcc 4.6 > is no longer supported). So if I understood correctly this bug affects only gcc-8? Or does it affect older version as well? From comment #3, Wilco stated it was fixed by on gcc-10, so I take it was backported to gcc-9 already (since you didn't see it on gcc-9). I did a sniff build tests with different gcc (8 and 9 mostly) on different architectures and it seems ok. LGTM with the just nit below about VERSYMIDX. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> > --- > note: with new gcc the code generation only changes > slightly on aarch64 (the code becomes a bit smaller), > with old gcc the change is not a robust fix for the > issue but it seems to be be sufficient in my testing. > > the change only expected to have minor effect on > other targets, since it's mostly cosmetic. > > elf/get-dynamic-info.h | 41 ++++++++++++++++++----------------------- > 1 file changed, 18 insertions(+), 23 deletions(-) > > diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h > index 4f9aac63de..d8b071dff5 100644 > --- a/elf/get-dynamic-info.h > +++ b/elf/get-dynamic-info.h > @@ -28,52 +28,47 @@ static > auto > #endif > inline void __attribute__ ((unused, always_inline)) > elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp) > { > - ElfW(Dyn) *dyn = l->l_ld; > - ElfW(Dyn) **info; > #if __ELF_NATIVE_CLASS == 32 > typedef Elf32_Word d_tag_utype; > #elif __ELF_NATIVE_CLASS == 64 > typedef Elf64_Xword d_tag_utype; > #endif > > #if !defined RTLD_BOOTSTRAP && !defined STATIC_PIE_BOOTSTRAP > - if (dyn == NULL) > + if (l->l_ld == NULL) > return; > #endif > > - info = l->l_info; > + ElfW(Dyn) **info = l->l_info; > Ok. > - while (dyn->d_tag != DT_NULL) > + for (ElfW(Dyn) *dyn = l->l_ld; dyn->d_tag != DT_NULL; dyn++) > { > + d_tag_utype i; > + > if ((d_tag_utype) dyn->d_tag < DT_NUM) > - info[dyn->d_tag] = dyn; > + i = dyn->d_tag; > else if (dyn->d_tag >= DT_LOPROC > && dyn->d_tag < DT_LOPROC + DT_THISPROCNUM) > - { > - /* This does not violate the array bounds of l->l_info, but > - gcc 4.6 on sparc somehow does not see this. */ > - DIAG_PUSH_NEEDS_COMMENT; > - DIAG_IGNORE_NEEDS_COMMENT (4.6, > - "-Warray-bounds"); > - info[dyn->d_tag - DT_LOPROC + DT_NUM] = dyn; > - DIAG_POP_NEEDS_COMMENT; > - } > + i = dyn->d_tag - DT_LOPROC + DT_NUM; Ok. > else if ((d_tag_utype) DT_VERSIONTAGIDX (dyn->d_tag) < DT_VERSIONTAGNUM) > - info[VERSYMIDX (dyn->d_tag)] = dyn; > + i = DT_VERSIONTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM; Why expand VERSYMIDX macro here? > else if ((d_tag_utype) DT_EXTRATAGIDX (dyn->d_tag) < DT_EXTRANUM) > - info[DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > - + DT_VERSIONTAGNUM] = dyn; > + i = DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > + + DT_VERSIONTAGNUM; Ok. > else if ((d_tag_utype) DT_VALTAGIDX (dyn->d_tag) < DT_VALNUM) > - info[DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > - + DT_VERSIONTAGNUM + DT_EXTRANUM] = dyn; > + i = DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > + + DT_VERSIONTAGNUM + DT_EXTRANUM; Ok. > else if ((d_tag_utype) DT_ADDRTAGIDX (dyn->d_tag) < DT_ADDRNUM) > - info[DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > - + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM] = dyn; > - ++dyn; > + i = DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > + + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM; > + else > + continue; > + > + info[i] = dyn; > } > > #define DL_RO_DYN_TEMP_CNT 8 > > #ifndef DL_RO_DYN_SECTION > Ok.
The 01/12/2021 14:52, Adhemerval Zanella wrote: > On 11/01/2021 12:11, Szabolcs Nagy via Libc-alpha wrote: > > Since commit 2f056e8a5dd4dc0f075413f931e82cede37d1057 > > "aarch64: define PI_STATIC_AND_HIDDEN", > > building glibc with gcc-8 on aarch64 fails with > > > > /BLD/elf/librtld.os: in function `elf_get_dynamic_info': > > /SRC/elf/get-dynamic-info.h:70:(.text+0xad8): relocation truncated to > > fit: R_AARCH64_ADR_PREL_PG_HI21 against symbol `_rtld_local' defined > > in .data section in /BLD/elf/librtld.os > > > > This is a gcc bug: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98618 > > > > Rewriting the affected code in elf_get_dynamic_info > > seems to make this issue go away on old gcc. > > > > The change makes the logic a bit clearer too (by > > separating the index computation and array update) > > and drops an older gcc workaround (since gcc 4.6 > > is no longer supported). > > So if I understood correctly this bug affects only gcc-8? Or > does it affect older version as well? From comment #3, Wilco stated affects gcc-7 and older gcc too, but i see this was not clear in my message. > it was fixed by on gcc-10, so I take it was backported to gcc-9 > already (since you didn't see it on gcc-9). it seems to affect gcc-9 too, but a change in how constants are constructed seems to make it less likely to hit. i'll update the description. > > I did a sniff build tests with different gcc (8 and 9 mostly) on > different architectures and it seems ok. > > LGTM with the just nit below about VERSYMIDX. > > Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> > ... > > - while (dyn->d_tag != DT_NULL) > > + for (ElfW(Dyn) *dyn = l->l_ld; dyn->d_tag != DT_NULL; dyn++) > > { > > + d_tag_utype i; > > + > > if ((d_tag_utype) dyn->d_tag < DT_NUM) > > - info[dyn->d_tag] = dyn; > > + i = dyn->d_tag; > > else if (dyn->d_tag >= DT_LOPROC > > && dyn->d_tag < DT_LOPROC + DT_THISPROCNUM) > > - { > > - /* This does not violate the array bounds of l->l_info, but > > - gcc 4.6 on sparc somehow does not see this. */ > > - DIAG_PUSH_NEEDS_COMMENT; > > - DIAG_IGNORE_NEEDS_COMMENT (4.6, > > - "-Warray-bounds"); > > - info[dyn->d_tag - DT_LOPROC + DT_NUM] = dyn; > > - DIAG_POP_NEEDS_COMMENT; > > - } > > + i = dyn->d_tag - DT_LOPROC + DT_NUM; > > Ok. > > else if ((d_tag_utype) DT_VERSIONTAGIDX (dyn->d_tag) < DT_VERSIONTAGNUM) > > - info[VERSYMIDX (dyn->d_tag)] = dyn; > > + i = DT_VERSIONTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM; > > Why expand VERSYMIDX macro here? > for the same reason VALIDX and ADDRIDX are not used below: i think this makes it clearer what's going on, you don't have to look up these convenience macros in ldsodefs.h to verify that the checks are right. but i can undo this change. > > else if ((d_tag_utype) DT_EXTRATAGIDX (dyn->d_tag) < DT_EXTRANUM) > > - info[DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > > - + DT_VERSIONTAGNUM] = dyn; > > + i = DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > > + + DT_VERSIONTAGNUM; > > Ok. > > > else if ((d_tag_utype) DT_VALTAGIDX (dyn->d_tag) < DT_VALNUM) > > - info[DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > > - + DT_VERSIONTAGNUM + DT_EXTRANUM] = dyn; > > + i = DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > > + + DT_VERSIONTAGNUM + DT_EXTRANUM; > > Ok. > > > else if ((d_tag_utype) DT_ADDRTAGIDX (dyn->d_tag) < DT_ADDRNUM) > > - info[DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > > - + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM] = dyn; > > - ++dyn; > > + i = DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM > > + + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM; > > + else > > + continue; > > + > > + info[i] = dyn; > > } > > > > #define DL_RO_DYN_TEMP_CNT 8 > > > > #ifndef DL_RO_DYN_SECTION > > > > Ok.
On 13/01/2021 06:10, Szabolcs Nagy wrote: > The 01/12/2021 14:52, Adhemerval Zanella wrote: >> On 11/01/2021 12:11, Szabolcs Nagy via Libc-alpha wrote: >>> Since commit 2f056e8a5dd4dc0f075413f931e82cede37d1057 >>> "aarch64: define PI_STATIC_AND_HIDDEN", >>> building glibc with gcc-8 on aarch64 fails with >>> >>> /BLD/elf/librtld.os: in function `elf_get_dynamic_info': >>> /SRC/elf/get-dynamic-info.h:70:(.text+0xad8): relocation truncated to >>> fit: R_AARCH64_ADR_PREL_PG_HI21 against symbol `_rtld_local' defined >>> in .data section in /BLD/elf/librtld.os >>> >>> This is a gcc bug: >>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98618 >>> >>> Rewriting the affected code in elf_get_dynamic_info >>> seems to make this issue go away on old gcc. >>> >>> The change makes the logic a bit clearer too (by >>> separating the index computation and array update) >>> and drops an older gcc workaround (since gcc 4.6 >>> is no longer supported). >> >> So if I understood correctly this bug affects only gcc-8? Or >> does it affect older version as well? From comment #3, Wilco stated > > affects gcc-7 and older gcc too, but i see this > was not clear in my message. > >> it was fixed by on gcc-10, so I take it was backported to gcc-9 >> already (since you didn't see it on gcc-9). > > it seems to affect gcc-9 too, but a change in how > constants are constructed seems to make it less > likely to hit. > > i'll update the description. Ok, thanks. > >> >> I did a sniff build tests with different gcc (8 and 9 mostly) on >> different architectures and it seems ok. >> >> LGTM with the just nit below about VERSYMIDX. >> >> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> >> > ... >>> - while (dyn->d_tag != DT_NULL) >>> + for (ElfW(Dyn) *dyn = l->l_ld; dyn->d_tag != DT_NULL; dyn++) >>> { >>> + d_tag_utype i; >>> + >>> if ((d_tag_utype) dyn->d_tag < DT_NUM) >>> - info[dyn->d_tag] = dyn; >>> + i = dyn->d_tag; >>> else if (dyn->d_tag >= DT_LOPROC >>> && dyn->d_tag < DT_LOPROC + DT_THISPROCNUM) >>> - { >>> - /* This does not violate the array bounds of l->l_info, but >>> - gcc 4.6 on sparc somehow does not see this. */ >>> - DIAG_PUSH_NEEDS_COMMENT; >>> - DIAG_IGNORE_NEEDS_COMMENT (4.6, >>> - "-Warray-bounds"); >>> - info[dyn->d_tag - DT_LOPROC + DT_NUM] = dyn; >>> - DIAG_POP_NEEDS_COMMENT; >>> - } >>> + i = dyn->d_tag - DT_LOPROC + DT_NUM; >> >> Ok. >>> else if ((d_tag_utype) DT_VERSIONTAGIDX (dyn->d_tag) < DT_VERSIONTAGNUM) >>> - info[VERSYMIDX (dyn->d_tag)] = dyn; >>> + i = DT_VERSIONTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM; >> >> Why expand VERSYMIDX macro here? >> > > for the same reason VALIDX and ADDRIDX are not used below: > i think this makes it clearer what's going on, you don't > have to look up these convenience macros in ldsodefs.h > to verify that the checks are right. > > but i can undo this change. I don't have a strong preference, but VERSYMIDX seems to be used in a lot of place so it makes sense to be used where applicable. > >>> else if ((d_tag_utype) DT_EXTRATAGIDX (dyn->d_tag) < DT_EXTRANUM) >>> - info[DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM >>> - + DT_VERSIONTAGNUM] = dyn; >>> + i = DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM >>> + + DT_VERSIONTAGNUM; >> >> Ok. >> >>> else if ((d_tag_utype) DT_VALTAGIDX (dyn->d_tag) < DT_VALNUM) >>> - info[DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM >>> - + DT_VERSIONTAGNUM + DT_EXTRANUM] = dyn; >>> + i = DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM >>> + + DT_VERSIONTAGNUM + DT_EXTRANUM; >> >> Ok. >> >>> else if ((d_tag_utype) DT_ADDRTAGIDX (dyn->d_tag) < DT_ADDRNUM) >>> - info[DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM >>> - + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM] = dyn; >>> - ++dyn; >>> + i = DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM >>> + + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM; >>> + else >>> + continue; >>> + >>> + info[i] = dyn; >>> } >>> >>> #define DL_RO_DYN_TEMP_CNT 8 >>> >>> #ifndef DL_RO_DYN_SECTION >>> >> >> Ok.
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h index 4f9aac63de..d8b071dff5 100644 --- a/elf/get-dynamic-info.h +++ b/elf/get-dynamic-info.h @@ -28,52 +28,47 @@ static auto #endif inline void __attribute__ ((unused, always_inline)) elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp) { - ElfW(Dyn) *dyn = l->l_ld; - ElfW(Dyn) **info; #if __ELF_NATIVE_CLASS == 32 typedef Elf32_Word d_tag_utype; #elif __ELF_NATIVE_CLASS == 64 typedef Elf64_Xword d_tag_utype; #endif #if !defined RTLD_BOOTSTRAP && !defined STATIC_PIE_BOOTSTRAP - if (dyn == NULL) + if (l->l_ld == NULL) return; #endif - info = l->l_info; + ElfW(Dyn) **info = l->l_info; - while (dyn->d_tag != DT_NULL) + for (ElfW(Dyn) *dyn = l->l_ld; dyn->d_tag != DT_NULL; dyn++) { + d_tag_utype i; + if ((d_tag_utype) dyn->d_tag < DT_NUM) - info[dyn->d_tag] = dyn; + i = dyn->d_tag; else if (dyn->d_tag >= DT_LOPROC && dyn->d_tag < DT_LOPROC + DT_THISPROCNUM) - { - /* This does not violate the array bounds of l->l_info, but - gcc 4.6 on sparc somehow does not see this. */ - DIAG_PUSH_NEEDS_COMMENT; - DIAG_IGNORE_NEEDS_COMMENT (4.6, - "-Warray-bounds"); - info[dyn->d_tag - DT_LOPROC + DT_NUM] = dyn; - DIAG_POP_NEEDS_COMMENT; - } + i = dyn->d_tag - DT_LOPROC + DT_NUM; else if ((d_tag_utype) DT_VERSIONTAGIDX (dyn->d_tag) < DT_VERSIONTAGNUM) - info[VERSYMIDX (dyn->d_tag)] = dyn; + i = DT_VERSIONTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM; else if ((d_tag_utype) DT_EXTRATAGIDX (dyn->d_tag) < DT_EXTRANUM) - info[DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM - + DT_VERSIONTAGNUM] = dyn; + i = DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM + + DT_VERSIONTAGNUM; else if ((d_tag_utype) DT_VALTAGIDX (dyn->d_tag) < DT_VALNUM) - info[DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM - + DT_VERSIONTAGNUM + DT_EXTRANUM] = dyn; + i = DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM + + DT_VERSIONTAGNUM + DT_EXTRANUM; else if ((d_tag_utype) DT_ADDRTAGIDX (dyn->d_tag) < DT_ADDRNUM) - info[DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM - + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM] = dyn; - ++dyn; + i = DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM + + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM; + else + continue; + + info[i] = dyn; } #define DL_RO_DYN_TEMP_CNT 8 #ifndef DL_RO_DYN_SECTION