Date: Sat, 24 May 2025 16:31:13 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 287050] Change in PTRACE_CONTINUE causing valgrind/vgdb to no longer be able to interrupt debuggee Message-ID: <bug-287050-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=287050 Bug ID: 287050 Summary: Change in PTRACE_CONTINUE causing valgrind/vgdb to no longer be able to interrupt debuggee Product: Base System Version: 15.0-CURRENT Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: pjfloyd@wanadoo.fr This is with FreeBSD freebsd 15.0-CURRENT FreeBSD 15.0-CURRENT #0 main-n277145-6ee513f4f26d: Thu May 8 05:11:14 UTC 2025 root@releng3.nyi.freebsd.org:/usr/obj/usr/src/amd64.amd64/sys/GENERIC amd64 Background ~~~~~~~~~~ When running Valgrind with vgdb gdb uses its remote protocol with vgdb in the following manner gdb <-pipe-> vgdb <-fifo-> valgrind If the user wants to interrupt the inferior with ctrl-C then the following should happen 1. gdb handles SIGINT and passes the relevant packet to vgdb 2. vgdb uses the same technique as gdb to invoke a function in Valgrind 2a. PTRACE_ATTACH to the Valgrind pid 2b. PTRACE_ GETREGS READ WRITE and SETREGS to setup a stack and RIP for the function to invoke 2c. PTRACE_CONTINUE to run the invoked function 3. The invoked Valgrind function does loads of hacky Valgrind things then passes control back to gdb Problem ~~~~~~~ I'm seeing the above process get as far as 2c on the vgdb side but I'm not seeing step 3 the invoked function running on the Valgrind side. Could this be related to https://reviews.freebsd.org/D49678 ? Small reproducer ~~~~~~~~~~~~~~~~ 1st terminal ------------ Run valgrind --tool=none --vgdb-error=0 -d sleep 100000 (the -d is optional for debug output) 2nd terminal ------------ Run gdb Then at the gdb prompt target remote | vgdb -d continue hit ctrl-c On 15-CURRENT I get the following output ^C18:27:14.880322 attach to 'main' pid 15004 18:27:14.880434 attach main pid PT_ATTACH pid 15004 18:27:14.880447 waitstopped attach main pid before waitpid signal_expected 17 18:27:14.880455 after waitpid pid 15004 p 15004 status 0x117f WIFSTOPPED 17 18:27:14.880460 calling getregs 18:27:14.880465 getregs call succeeded 18:27:14.880469 push bad_return return address ptrace_write_memory 18:27:14.880472 Writing 0000000000000000 to 0x100288dd48 18:27:14.880489 calling setregs 18:27:14.880493 setregs succeeded 18:27:14.880495 PT_CONTINUE to invoke 18:27:14.880500 waitstopped waitpid status after PTRACE_CONT to invoke before waitpid signal_expected 17 but no gdb prompt On 14-2-RELEASE I get similar output but it continues to the gdb prompt: Program received signal SIGTRAP, Trace/breakpoint trap. _nanosleep () at _nanosleep.S:4 warning: 4 _nanosleep.S: No such file or directory (gdb) Additionally on 14.2 (but not 15) I get on the Valgrind side in the 1st terminal --72512:1: gdbsrv invoke_gdbserver running_tid 0 vgdb_interrupted_tid 1 --72512:1: gdbsrv entering call_gdbserver vgdb_reason ... pid 72512 tid 1 status VgTs_WaitSys sched_jmpbuf_valid 1 --72512:1: gdbsrv enter valgrind_wait pid 72512 --72512:1: gdbsrv stop pc is 0x498553A --72512:1: gdbsrv exit valgrind_wait status T ptid id 107814 stop_pc 0x498553A: _nanosleep (in /lib/libc.so.7) signal 5 --72512:1: gdbsrv Writing resume reply for 107814 --72512:1: gdbsrv remove software_breakpoint at addr 0x400FCA0 0x400FCA0: r_debug_state (in /libexec/ld-elf.so.1) -- You are receiving this mail because: You are the assignee for the bug.home | help
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