dynamic: x86 64: Support runtime dynamic unpatching #1748
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Originally, when the user asks to only unpatch functions, uftrace would patch all other functions by default. This is counter-intuitive, especially when using the agent to unpatch at runtime. The user doesn't expect functions to be patched when they only unpatch funtions. This commit removes this behavior, and requires the user to explicitly define functions to patch. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
Libmcount would try to unpatch by default any function that is not matched by the user patch or unpatch options. We remove this implicit behavior, so the user explicitly choses which function to unpatch. Signed-off-by: Clément Guidi <cguidi@ciena.com>
Return whether a symbol is positively or negatively matched against a pattern list, or not matched at all. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
Glibc < 2.30 doen't provide wrappers for 'gettid()' and 'tgkill()' so we define them. Signed-off-by: Clément Guidi <cguidi@ciena.com>
Functions to setup real-time signals and broadcast signals to all threads in an application. Useful for runtime synchronization mechanisms. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
Skip the functions where uftrace already injected a call to a trampoline. Signed-off-by: Clément Guidi <cguidi@ciena.com>
Refactor for more clarity. Signed-off-by: Clément Guidi <cguidi@ciena.com>
Refactor 'patch_code' so it can later be used at runtime. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
Check if instruction at a given address is ENDBR64. Signed-off-by: Clément Guidi <cguidi@ciena.com>
When patching a function at runtime, first insert an int3 trap so any incoming thread is diverted from the patching region, to avoid executing partially modified code. The trap handler emulates a call to the trampoline, thus enabling the instrumentation. The trap is eventually removed in subsequent commits. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
When cross-modifying code, the software needs to ensure that all cores will execute valid instructions at any time. When modifications are not atomic, we issue a specific memory barrier (or execute a serializing instruction on Linux < 4.16) to serialize the execution across all cores. This flushes the different caches, especially the processor pipelines that may have partially fetched straddling instructions. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
When patching at runtime, no thread can enter the patching region due to the trap that is inserted at the start of it. But threads that entered the region before the trap is installed can still be executing instructions in the region. We broadcast a real-time signal instruction all threads to check their instruction pointer, and execute out-of-line if they are in the patching region. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
Synchronization requires sending signals to threads inside the process. This is performed for every symbols, which means a lot of signal can be sent. This has a major performance impact. This commit batches the initial and final steps of the patching process so we only need to send one signal per thread for every batch. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
This commit add for dynamically unpatching functions for the x86_64 architecture. The process is executed concurrently by replacing using a trap to resolve race conditions between thread (similar to how optimized kprobes are done). Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
Synchronization requires sending signals to threads inside the process. This is performed for every symbols, which means a lot of signal can be sent. This has a major performance impact. This commit batches the initial and final steps of the patching process so we only need to send one signal per thread for every batch. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <gabrielpolloguilbert@gmail.com> Signed-off-by: Clément Guidi <cguidi@ciena.com>
This was referenced Jul 7, 2023
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This is the eight PR in a series of patches intended to bring runtime dynamic tracing on x86_64 to uftrace.
We add support for removing dynamically inserted tracepoints from a running application. The strategy is similar to patching, expect we replace instrumentation with the original code.
Related: #1698