dynamic: x86_64: Fall back to original patching strategy when target is not running #1750
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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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
Glibc < 2.30 doen't provide wrappers for 'gettid()' and 'tgkill()' so we define them. Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
Skip the functions where uftrace already injected a call to a trampoline. Signed-off-by: Clément Guidi <[email protected]>
Refactor for more clarity. Signed-off-by: Clément Guidi <[email protected]>
Refactor 'patch_code' so it can later be used at runtime. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
Check if instruction at a given address is ENDBR64. Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
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 <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
Add support for the '--patch' and '--unpatch' options in the client. When used, the agent patches or unpatches symbols on the fly. Co-authored-by: Gabriel-Andrew Pollo-Guilbert <[email protected]> Signed-off-by: Clément Guidi <[email protected]>
Use a global flag to indicate the state of the target. When the target is not running, tasks such as dynamic patching can be performed with less constraints. If libmcount.so is dynamically injected (not implemented yet), the 'mcount_target_running' flag indicates that libmcount has to be initialized in a running target. Signed-off-by: Clément Guidi <[email protected]>
When patching a binary before its execution, we can skip the serialization and critical zone exclusion steps. These steps are only use full when cross-modification occurs, at runtime. Signed-off-by: Clément Guidi <[email protected]>
This was referenced Jul 7, 2023
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This is the tenth PR in a series of patches intended to bring runtime dynamic tracing on x86_64 to uftrace.
We only apply the runtime dynamic instrumentation strategy when the target is running. Otherwise, we fall back to the original strategy (no cross-modification).
Related: #1698