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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 ... commit 8c95582da8 "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 ... commit d8cc8af6a1 "[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 commit d8cc8af6a1 was 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 commit d8cc8af6a1, 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.
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.