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author | Florian Weimer <fweimer@redhat.com> | 2022-11-04 10:18:03 +0100 |
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committer | Florian Weimer <fweimer@redhat.com> | 2022-11-04 10:18:03 +0100 |
commit | e724b0480bfa5ec04f39be8c7290330b495c59de (patch) | |
tree | b6386f6ca91a728a373e2c2bdaeb901b83aa3683 /libgcc | |
parent | a05d8e1d15ea08526639ba154e59b6822b704f4c (diff) | |
download | gcc-e724b0480bfa5ec04f39be8c7290330b495c59de.zip gcc-e724b0480bfa5ec04f39be8c7290330b495c59de.tar.gz gcc-e724b0480bfa5ec04f39be8c7290330b495c59de.tar.bz2 |
libgcc: Special-case BFD ld unwind table encodings in find_fde_tail
BFD ld (and the other linkers) only produce one encoding of these
values. It is not necessary to use the general
read_encoded_value_with_base decoding routine. This avoids the
data-dependent branches in its implementation.
libgcc/
* unwind-dw2-fde-dip.c (find_fde_tail): Special-case encoding
values actually used by BFD ld.
Diffstat (limited to 'libgcc')
-rw-r--r-- | libgcc/unwind-dw2-fde-dip.c | 58 |
1 files changed, 48 insertions, 10 deletions
diff --git a/libgcc/unwind-dw2-fde-dip.c b/libgcc/unwind-dw2-fde-dip.c index 7f9be5e..f370c12 100644 --- a/libgcc/unwind-dw2-fde-dip.c +++ b/libgcc/unwind-dw2-fde-dip.c @@ -396,10 +396,21 @@ find_fde_tail (_Unwind_Ptr pc, if (hdr->version != 1) return NULL; - p = read_encoded_value_with_base (hdr->eh_frame_ptr_enc, - base_from_cb_data (hdr->eh_frame_ptr_enc, - dbase), - p, &eh_frame); + if (__builtin_expect (hdr->eh_frame_ptr_enc == (DW_EH_PE_sdata4 + | DW_EH_PE_pcrel), 1)) + { + /* Specialized version of read_encoded_value_with_base, based on what + BFD ld generates. */ + signed value __attribute__ ((mode (SI))); + memcpy (&value, p, sizeof (value)); + p += sizeof (value); + dbase = value; /* No adjustment because pcrel has base 0. */ + } + else + p = read_encoded_value_with_base (hdr->eh_frame_ptr_enc, + base_from_cb_data (hdr->eh_frame_ptr_enc, + dbase), + p, &eh_frame); /* We require here specific table encoding to speed things up. Also, DW_EH_PE_datarel here means using PT_GNU_EH_FRAME start @@ -409,10 +420,20 @@ find_fde_tail (_Unwind_Ptr pc, { _Unwind_Ptr fde_count; - p = read_encoded_value_with_base (hdr->fde_count_enc, - base_from_cb_data (hdr->fde_count_enc, - dbase), - p, &fde_count); + if (__builtin_expect (hdr->fde_count_enc == DW_EH_PE_udata4, 1)) + { + /* Specialized version of read_encoded_value_with_base, based on + what BFD ld generates. */ + unsigned value __attribute__ ((mode (SI))); + memcpy (&value, p, sizeof (value)); + p += sizeof (value); + fde_count = value; + } + else + p = read_encoded_value_with_base (hdr->fde_count_enc, + base_from_cb_data (hdr->fde_count_enc, + dbase), + p, &fde_count); /* Shouldn't happen. */ if (fde_count == 0) return NULL; @@ -454,8 +475,25 @@ find_fde_tail (_Unwind_Ptr pc, f = (fde *) (table[mid].fde + data_base); f_enc = get_fde_encoding (f); f_enc_size = size_of_encoded_value (f_enc); - read_encoded_value_with_base (f_enc & 0x0f, 0, - &f->pc_begin[f_enc_size], &range); + + /* BFD ld uses DW_EH_PE_sdata4 | DW_EH_PE_pcrel on non-FDPIC targets, + so optimize for that. + + This optimization is not valid for FDPIC targets. f_enc & 0x0f as + passed to read_encoded_value_with_base masks away the base flags, + but they are implicit for FDPIC. */ +#ifndef __FDPIC__ + if (__builtin_expect (f_enc == (DW_EH_PE_sdata4 | DW_EH_PE_pcrel), + 1)) + { + signed value __attribute__ ((mode (SI))); + memcpy (&value, &f->pc_begin[f_enc_size], sizeof (value)); + range = value; + } + else +#endif + read_encoded_value_with_base (f_enc & 0x0f, 0, + &f->pc_begin[f_enc_size], &range); _Unwind_Ptr func = table[mid].initial_loc + data_base; if (pc < table[mid].initial_loc + data_base + range) { |