Date: Sat, 1 Oct 2022 19:00:15 +0300 From: Christos Margiolis <christos@freebsd.org> To: freebsd-hackers@freebsd.org Cc: markj@freebsd.org Subject: Instruction-level dynamic tracing Message-ID: <20221001160015.sce47pwwtqu62vcr@pleb>
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Hello, Me and markj@ implemented a new DTrace provider (kinst) that allows for arbitrary kernel instruction tracing. The provider is currently implemented only for amd64, but we plan to port it to other architectures in the future as well. kinst probes take the form of: kinst:<module>:<function>:<offset> where "function" is the kernel function to be traced, and "offset" is the offset to a specific instruction. This offset can be obtained from the function's disassembly using kgdb. For example, if I want to trace the second instruction in amd64_syscall(), I first need to figure out the offset to the second instruction: # kgdb (kgdb) disas /r amd64_syscall Dump of assembler code for function amd64_syscall: 0xffffffff809256c0 <+0>: 55 push %rbp 0xffffffff809256c1 <+1>: 48 89 e5 mov %rsp,%rbp 0xffffffff809256c4 <+4>: 41 57 push %r15 The offset is 1. To trace it: # dtrace -n 'kinst::amd64_syscall:1' Final code review: https://reviews.freebsd.org/D36851 Any review of the code would be appreciated. Christos
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