Add global variable example #51
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Signed-off-by: Alan Jowett <[email protected]>
WalkthroughThe pull request introduces a new source file Changes
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Actionable comments posted: 2
🧹 Nitpick comments (1)
src/global_variable.c (1)
1-13: Add documentation explaining the purpose of global variablesAdd comments explaining:
- Purpose of these global variables
- Expected access patterns
- Synchronization guarantees
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⛔ Files ignored due to path filters (1)
build/global_variable.ois excluded by!**/*.o
📒 Files selected for processing (2)
CMakeLists.txt(2 hunks)src/global_variable.c(1 hunks)
🔇 Additional comments (1)
CMakeLists.txt (1)
28-28: LGTM
Build configuration follows the established pattern and includes appropriate compilation flags.
Also applies to: 97-99
Signed-off-by: Alan Jowett <[email protected]>
Signed-off-by: Alan Jowett <[email protected]>
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Actionable comments posted: 0
🧹 Nitpick comments (1)
src/global_variable.c (1)
6-11: Add example usage to the documentationThe comments explain the requirements well. Consider adding a brief example of how this module should be used by other BPF programs.
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⛔ Files ignored due to path filters (1)
build/global_variable.ois excluded by!**/*.o
📒 Files selected for processing (1)
src/global_variable.c(1 hunks)
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📓 Learnings (1)
src/global_variable.c (2)
Learnt from: Alan-Jowett
PR: vbpf/ebpf-samples#51
File: src/global_variable.c:9-13
Timestamp: 2024-12-16T18:26:29.968Z
Learning: In the `src/global_variable.c` file of the `ebpf-samples` project, the functions `atomic_inc` and `atomic_add` are not defined or available.
Learnt from: Alan-Jowett
PR: vbpf/ebpf-samples#51
File: src/global_variable.c:6-7
Timestamp: 2024-12-16T18:26:11.366Z
Learning: In eBPF programs, the `atomic_t` type isn't valid; instead, use atomic built-in functions like `__sync_fetch_and_add` for atomic operations on global variables.
🔇 Additional comments (3)
src/global_variable.c (3)
1-4: LGTM: License header is properly formatted
12-13: LGTM: Global variables are properly declared
The volatile keyword and uint32_t type are appropriate for atomic operations.
15-19: Mark unused parameter with attribute((unused))
The ctx parameter is required by the BPF program signature but not used in the function.
-int func(void* ctx) {
+int func(void* ctx __attribute__((unused))) {
__sync_fetch_and_add(&global_var, 1);
__sync_fetch_and_add(&global_var_2, 2);
return 0;
}✅ Verification successful
Mark unused parameter with attribute((unused))
The suggestion is valid. The search results confirm that:
- The
void* ctxparameter signature is consistently used across multiple BPF programs in the codebase - The parameter is often left unused, as seen in simple programs like
func0,func1in prog_array.c - When used, the parameter is accessed for BPF context operations
- Add
__attribute__((unused))tosrc/global_variable.c:func()to silence compiler warnings about the unused parameter while maintaining the required BPF program signature
🏁 Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash
# Verify that the function signature matches BPF program requirements
ast-grep --pattern 'int $func(void* $_) { $$$ }'
Length of output: 50
Script:
#!/bin/bash
# Search for BPF program signatures in C files
rg -t c "int.*\(void\*.*\)" -A 2
# Look for similar functions with unused attribute
rg -t c "__attribute__\(\(unused\)\)"
Length of output: 2655
This pull request includes updates to the build configuration and the addition of a new source file. The most important changes include adding a new object file to the build process and creating a new source file with its corresponding build command.
Build configuration updates:
CMakeLists.txt: Addedglobal_variable.oto the list of object files in theadd_custom_target(samples ALLcommand.CMakeLists.txt: Added a newadd_custom_commandfor buildingglobal_variable.ofromglobal_variable.c.New source file:
src/global_variable.c: Added a new source file defining two global variables and a function that modifies these variables.Summary by CodeRabbit
New Features
Bug Fixes