From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2178) id 61142385840D; Fri, 4 Nov 2022 09:19:06 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 61142385840D DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1667553547; bh=yDItIE+i5/Q+2oS8TfmgKRkxXt3GgSjKAG313LuG/qs=; h=From:To:Subject:Date:From; b=C5ZuNjAoZZ9hTIxzCKUFE6MUXWgjGs3bJsEtMFvTzHsrtEbdhcNSHMrPD4wYkdape A64yrhj9jMz6/cbzIeazYRZzYN4IvKBPh/epaUul9oJ4lm8pk9jIQnYVxcgCh5530N kx7+LgcOAHjGv6cfMFIc6kza0JjQJrVAsXibIqHE= MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Florian Weimer To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-3651] libgcc: Special-case BFD ld unwind table encodings in find_fde_tail X-Act-Checkin: gcc X-Git-Author: Florian Weimer X-Git-Refname: refs/heads/master X-Git-Oldrev: a05d8e1d15ea08526639ba154e59b6822b704f4c X-Git-Newrev: e724b0480bfa5ec04f39be8c7290330b495c59de Message-Id: <20221104091907.61142385840D@sourceware.org> Date: Fri, 4 Nov 2022 09:19:06 +0000 (GMT) List-Id: https://gcc.gnu.org/g:e724b0480bfa5ec04f39be8c7290330b495c59de commit r13-3651-ge724b0480bfa5ec04f39be8c7290330b495c59de Author: Florian Weimer Date: Fri Nov 4 10:18:03 2022 +0100 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. Diff: --- libgcc/unwind-dw2-fde-dip.c | 58 +++++++++++++++++++++++++++++++++++++-------- 1 file changed, 48 insertions(+), 10 deletions(-) diff --git a/libgcc/unwind-dw2-fde-dip.c b/libgcc/unwind-dw2-fde-dip.c index 7f9be5e6b02..f370c1279ae 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) {