From b2e586e850dbf1dafc10beea3250d22e70add4b5 Mon Sep 17 00:00:00 2001 From: Simon Marchi Date: Sat, 7 Apr 2018 13:51:59 -0400 Subject: [PATCH] Defer breakpoint reset when cloning progspace for fork child Using this simple test: static void break_here () { } int main (int argc, char *argv[]) { fork (); break_here(); return 0; } compiled as a PIE: $ gcc test.c -g3 -O0 -o test -pie and running this: $ ./gdb -nx -q --data-directory=data-directory ./test -ex "b break_here" -ex "set detach-on-fork off" -ex r gives: Warning: Cannot insert breakpoint 1. Cannot access memory at address 0x64a Note that GDB might get stopped by SIGTTOU because of this issue: https://sourceware.org/bugzilla/show_bug.cgi?id=23020 In that case, just use "fg" to continue. This issue happens only with position-independent executables. Adding the main objfile for the new inferior (the fork child) causes GDB to try to reset the breakpoints. However, that new objfile has not been relocated yet. So the breakpoint on "break_here" resolves to an unrelocated address, from which we are trying to read/write to set a breakpoint. Passing SYMFILE_DEFER_BP_RESET avoids that problem. The executable is relocated just after, in the follow_fork_inferior function. The buildbot seems happy with this patch. I don't think it's necessary to add a new test. Just changing this made many tests go from FAIL to PASS on my machine, where gcc produces PIE executables by default. If anything, I think we would need to add a board file that produces position-independent executables, so that we can run all the tests with PIE, even on machines where that is not the default. gdb/ChangeLog: * progspace.c (clone_program_space): Pass SYMFILE_DEFER_BP_RESET to symbol_file_add_main. --- gdb/ChangeLog | 5 +++++ gdb/progspace.c | 3 ++- 2 files changed, 7 insertions(+), 1 deletion(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 4ffa4e7041d..47d28e3747e 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2018-04-07 Simon Marchi + + * progspace.c (clone_program_space): Pass SYMFILE_DEFER_BP_RESET + to symbol_file_add_main. + 2018-04-07 Simon Marchi PR mi/22299 diff --git a/gdb/progspace.c b/gdb/progspace.c index e0bcc5a18d6..ba400d47aa5 100644 --- a/gdb/progspace.c +++ b/gdb/progspace.c @@ -166,7 +166,8 @@ clone_program_space (struct program_space *dest, struct program_space *src) exec_file_attach (src->pspace_exec_filename, 0); if (src->symfile_object_file != NULL) - symbol_file_add_main (objfile_name (src->symfile_object_file), 0); + symbol_file_add_main (objfile_name (src->symfile_object_file), + SYMFILE_DEFER_BP_RESET); return dest; } -- 2.30.2