tools/javaobjnew: Use MIN macro instead of min function #5406
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The function min() is called among the arguments of
bpf_probe_read_user(). Depending on kernel version, the expansion of
the macro may emmit a fake function that prevent the compilation of
the BPF code.
Replace the min() function by the MIN() macro to solve the issue. This
is safe since both members of the comparison are unsigned integer.
Solves the following error:
/virtual/main.c:48:36: error: cannot call non-static helper function
48 | bpf_probe_read_user(&key.name, min(sizeof(key.name), (size_t)length), (void *)classptr);
| ^
include/linux/minmax.h:129:19: note: expanded from macro 'min'
129 | #define min(x, y) __careful_cmp(min, x, y)
| ^
include/linux/minmax.h:105:2: note: expanded from macro '__careful_cmp'
105 | __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
| ^
include/linux/minmax.h:100:2: note: expanded from macro '__careful_cmp_once'
100 | BUILD_BUG_ON_MSG(!__types_ok(x,y,ux,uy), \
| ^
note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
include/linux/compiler_types.h:418:2: note: expanded from macro '_compiletime_assert'
418 | __compiletime_assert(condition, msg, prefix, suffix)
| ^
include/linux/compiler_types.h:411:4: note: expanded from macro '__compiletime_assert'
411 | prefix ## suffix(); \
| ^
<scratch space>:91:1: note: expanded from here
91 | __compiletime_assert_317
| ^
1 error generated.
Traceback (most recent call last):
File "/usr/share/bcc/tools/lib/uobjnew", line 178, in <module>
bpf = BPF(text=program, usdt_contexts=[usdt])
File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 507, in __init__
raise Exception("Failed to compile BPF module %s" % (src_file or "<text>"))
Exception: Failed to compile BPF module <text>
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
ekyooo
reviewed
Oct 13, 2025
| bpf_usdt_readarg(3, ctx, &length); | ||
| bpf_usdt_readarg(4, ctx, &size); | ||
| bpf_probe_read_user(&key.name, min(sizeof(key.name), (size_t)length), (void *)classptr); | ||
| bpf_probe_read_user(&key.name, MIN(sizeof(key.name), (size_t)length), (void *)classptr); |
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If the content stored in key.name is confirmed to be a NUL-terminated string, would it be possible to replace bpf_probe_read_user with bpf_probe_read_user_str (without the MIN macro)?
There was a problem hiding this comment.
I don't know about this one: searching for the object__alloc usdt probe returns surprisingly few results.
Using bpf_probe_read_user_str() seems to work.
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The function min() is called among the arguments of bpf_probe_read_user(). Depending on kernel version, the expansion of the macro may emmit a fake function that prevent the compilation of the BPF code.
Replace the min() function by the MIN() macro to solve the issue. This is safe since both members of the comparison are unsigned integer.
Solves the following error:
/virtual/main.c:48:36: error: cannot call non-static helper function
48 | bpf_probe_read_user(&key.name, min(sizeof(key.name), (size_t)length), (void *)classptr);
| ^
include/linux/minmax.h:129:19: note: expanded from macro 'min'
129 | #define min(x, y) __careful_cmp(min, x, y)
| ^
include/linux/minmax.h:105:2: note: expanded from macro '__careful_cmp'
105 | __careful_cmp_once(op, x, y, _UNIQUE_ID(x), _UNIQUE_ID(y))
| ^
include/linux/minmax.h:100:2: note: expanded from macro '__careful_cmp_once'
100 | BUILD_BUG_ON_MSG(!__types_ok(x,y,ux,uy),
| ^
note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
include/linux/compiler_types.h:418:2: note: expanded from macro '_compiletime_assert'
418 | __compiletime_assert(condition, msg, prefix, suffix)
| ^
include/linux/compiler_types.h:411:4: note: expanded from macro '__compiletime_assert'
411 | prefix ## suffix();
| ^
:91:1: note: expanded from here
91 | __compiletime_assert_317
| ^
1 error generated.
Traceback (most recent call last):
File "/usr/share/bcc/tools/lib/uobjnew", line 178, in
bpf = BPF(text=program, usdt_contexts=[usdt])
File "/usr/lib/python3.9/site-packages/bcc/init.py", line 507, in init
raise Exception("Failed to compile BPF module %s" % (src_file or ""))
Exception: Failed to compile BPF module