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The DWARF standard states for the line register in the line number information state machine the following: ... An unsigned integer indicating a source line number. Lines are numbered beginning at 1. The compiler may emit the value 0 in cases where an instruction cannot be attributed to any source line. ... So, it's possible to have a zero line number in the DWARF line table. This is currently not handled by GDB. The zero value is read in as any other line number, but internally the zero value has a special meaning: end-of-sequence, so the line table entry ends up having a different interpretation than intended in some situations. I've created a test-case where various aspects are tested, which has these 4 interesting tests. 1. Next-step through a zero-line instruction, is_stmt == 1 gdb.dwarf2/dw2-line-number-zero.exp: bar1, 2nd next 2. Next-step through a zero-line instruction, is_stmt == 0 gdb.dwarf2/dw2-line-number-zero.exp: bar2, 2nd next 3. Show source location at zero-line instruction, is_stmt == 1 gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar1_label_3 4. Show source location at zero-line instruction, is_stmt == 0 gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar2_label_3 And we have the following results: 8.3.1, 9.2: ... FAIL: gdb.dwarf2/dw2-line-number-zero.exp: bar1, 2nd next PASS: gdb.dwarf2/dw2-line-number-zero.exp: bar2, 2nd next PASS: gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar1_label_3 FAIL: gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar2_label_3 ... commit8c95582da8"gdb: Add support for tracking the DWARF line table is-stmt field": ... PASS: gdb.dwarf2/dw2-line-number-zero.exp: bar1, 2nd next PASS: gdb.dwarf2/dw2-line-number-zero.exp: bar2, 2nd next FAIL: gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar1_label_3 FAIL: gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar2_label_3 ... commitd8cc8af6a1"[gdb/symtab] Fix line-table end-of-sequence sorting", master: FAIL: gdb.dwarf2/dw2-line-number-zero.exp: bar1, 2nd next FAIL: gdb.dwarf2/dw2-line-number-zero.exp: bar2, 2nd next PASS: gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar1_label_3 PASS: gdb.dwarf2/dw2-line-number-zero.exp: continue to breakpoint: bar2_label_3 ... The regression in test 2 at commitd8cc8af6a1was filed as PR symtab/26243, where clang emits zero line numbers. The way to fix all tests is to make sure line number zero internally doesn't clash with special meaning values, and by handling it appropriately everywhere. That however looks too intrusive for the GDB 10 release. Instead, we decide to ensure defined behaviour for line number zero by ignoring it. This gives us back the test results from before commitd8cc8af6a1, fixing PR26243. We mark the FAILs for tests 3 and 4 as KFAILs. Test 4 was already failing for the 9.2 release, and we consider the regression of test 3 from gdb 9.2 to gdb 10 the cost for having defined behaviour. Build and reg-tested on x86_64-linux. gdb/ChangeLog: 2020-07-25 Tom de Vries <tdevries@suse.de> PR symtab/26243 * dwarf2/read.c (lnp_state_machine::record_line): Ignore zero line entries. gdb/testsuite/ChangeLog: 2020-07-25 Tom de Vries <tdevries@suse.de> PR symtab/26243 * gdb.dwarf2/dw2-line-number-zero.c: New test. * gdb.dwarf2/dw2-line-number-zero.exp: New file.
63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
/*
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Copyright 2020 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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void
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foo (int x)
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{
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}
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void
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bar1 (void)
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{
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asm ("bar1_label: .globl bar1_label");
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foo (1);
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asm ("bar1_label_2: .globl bar1_label_2");
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foo (2);
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asm ("bar1_label_3: .globl bar1_label_3");
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foo (3);
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asm ("bar1_label_4: .globl bar1_label_4");
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foo (4);
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asm ("bar1_label_5: .globl bar1_label_5");
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}
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void
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bar2 (void)
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{
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asm ("bar2_label: .globl bar2_label");
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foo (1);
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asm ("bar2_label_2: .globl bar2_label_2");
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foo (2);
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asm ("bar2_label_3: .globl bar2_label_3");
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foo (3);
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asm ("bar2_label_4: .globl bar2_label_4");
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foo (4);
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asm ("bar2_label_5: .globl bar2_label_5");
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}
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int
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main (void)
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{
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asm ("main_label: .globl main_label");
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bar1 ();
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bar2 ();
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return 0;
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}
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