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Fixed issue #128882: don't warn if 1st argument to 'getcwd' is NULL #135720

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Fixed issue #128882: don't warn if 1st argument to 'getcwd' is NULL #135720

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1 change: 0 additions & 1 deletion clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2663,7 +2663,6 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
.Case({ArgumentCondition(1, WithinRange, Range(1, SizeMax)),
IsNull(Ret)},
ErrnoNEZeroIrrelevant, GenericFailureMsg)
.ArgConstraint(NotNull(ArgNo(0)))
.ArgConstraint(
BufferSize(/*Buffer*/ ArgNo(0), /*BufSize*/ ArgNo(1)))
.ArgConstraint(
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3 changes: 0 additions & 3 deletions clang/test/Analysis/errno-stdlibraryfunctions.c
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Original file line number Diff line number Diff line change
Expand Up @@ -105,9 +105,6 @@ void errno_getcwd(char *Buf, size_t Sz) {
clang_analyzer_eval(errno != 0); // expected-warning{{TRUE}}
clang_analyzer_eval(Path == NULL); // expected-warning{{TRUE}}
if (errno) {} // no warning
} else if (Path == NULL) {
clang_analyzer_eval(errno != 0); // expected-warning{{TRUE}}
if (errno) {} // no warning
Comment on lines -108 to -110
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Why did you drop this branch?

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@seanm seanm Apr 17, 2025 •
edited
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It caused a build/test warning/error here on github, I was hoping this was the correct fix. But I don't know the llvm codebase at all...

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Alright. I think I understand this now.

Because of ReturnValueCondition(BO_EQ, ArgNo(0)) on the success path we assume that the returned pointer is the same (aka. equal to) the first argument, which means that Path holds the same pointer as Buf.
Because of this, dropping the ArgConstraint(NotNull(ArgNo(0))) means that no longer affects the return value Path. This is actually a good thing.

Could you please help me how does the test failure look like for you if you would keep this hunk?

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Does the github CI delete previous results after I updated the PR? I can't find it here anymore...

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Oh, indeed it was there:

Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
c:\ws\src\build\bin\clang.exe -cc1 -internal-isystem C:\ws\src\build\lib\clang\21\include -nostdsysteminc -analyze -analyzer-constraints=range -setup-static-analyzer -verify C:\ws\src\clang\test\Analysis\errno-stdlibraryfunctions.c    -analyzer-checker=core    -analyzer-checker=debug.ExprInspection    -analyzer-checker=unix.StdCLibraryFunctions    -analyzer-checker=apiModeling.Errno    -analyzer-checker=unix.Errno    -analyzer-config unix.StdCLibraryFunctions:ModelPOSIX=true
# executed command: 'c:\ws\src\build\bin\clang.exe' -cc1 -internal-isystem 'C:\ws\src\build\lib\clang\21\include' -nostdsysteminc -analyze -analyzer-constraints=range -setup-static-analyzer -verify 'C:\ws\src\clang\test\Analysis\errno-stdlibraryfunctions.c' -analyzer-checker=core -analyzer-checker=debug.ExprInspection -analyzer-checker=unix.StdCLibraryFunctions -analyzer-checker=apiModeling.Errno -analyzer-checker=unix.Errno -analyzer-config unix.StdCLibraryFunctions:ModelPOSIX=true
# .---command stderr------------
# | error: 'expected-warning' diagnostics seen but not expected: 
# |   File C:\ws\src\clang\test\Analysis\errno-stdlibraryfunctions.c Line 109: FALSE [debug.ExprInspection]
# | 1 error generated.
# `-----------------------------
# error: command failed with exit status: 1

--

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Hmm, frankly, I do not follow. Seems this is a case where fixing the tests is harder than fixing the actual bug.

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Ping @balazske

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I checked the issue 128882, it references to the macOS man page for getcwd where a NULL buf argument is allowed. This is different from the original POSIX documentation where "the behavior of getcwd() is unspecified" if buf is NULL. This is why the condition is there. But "unspecified" does not mean invalid, so it may be correct to drop this requirement. But we must check how this affects the BufferSizeConstraint.

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It's not just macOS.

linux's glibc's "allocates the buffer dynamically using malloc if buf is NULL."

And FreeBSD: If buf is NULL, space is allocated as necessary to store the pathname. This space may later be free'd.

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The correct fix would be probably to add ArgumentConditions for the parameter 0 to be non-null in the existing "Case"-s, and add extra cases for the buf == NULL condition (where size is ignored but the return value can be still NULL on error or non-NULL on success).

} else {
clang_analyzer_eval(Path == Buf); // expected-warning{{TRUE}}
if (errno) {} // expected-warning{{An undefined value may be read from 'errno'}}
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