Fix strchr qualifier issues with C23.
The patch series fixes build errors due to implicit const conversions when compiling binutils with GCC 16.1 in C23 mode.
With GCC 16.1 defaulting to C23, the stricter constness of functions like strchr in glibc 2.43 trigger -Werror=discarded-qualifiers errors in binutils. This patch series updates calls to strchr and similar functions to handle the const char * return type when given a const char * argument. This resolves build failures and ensures compatibility with the updated C standard and glibc.
- proposer
Proposes to fix discarded qualifier errors when compiling binutils with GCC 16.1 in C23 mode due to stricter constness of functions like strchr.
“GCC 16.1 defaults to C23 and glibc 2.43 added const qualifiers to serveral functions. In particular strchr will now return a const char * when a const char * is given as input (and a char * when given a char * as input).”
- reviewer
Acknowledges the first patch and points out a similar error in `gprof/source.c`.
- reviewer
Confirms one patch has been checked in, and provides another patch for a similar error related to DOS-based filesystems.
“Well, one of them was. > Fix the strrchr error like: > > gprof/source.c:130:28: error: initialization discards ‘const’ > qualifier from pointer target type [-Werror=discarded-qualifiers] > 130 | char *bslash = strrchr (sf->name, '\');”
Technical Tradeoffs
- Code changes needed to accommodate the new constness may introduce subtle bugs if not handled carefully.
- Ignoring the warnings could lead to undefined behavior if the code attempts to modify a const string.
- The fix might require casting away constness in some cases, which should be done with caution.
In Details
Binutils uses strchr and related functions to manipulate strings. With C23 and newer glibc versions, these functions now return const char * when passed a const char *. This requires changes in binutils code to avoid discarding the const qualifier, which is enforced by -Werror.
For Context
binutils is a collection of tools used for working with binary files, including the linker (ld), assembler (as), and other utilities. The C standard library provides functions like strchr for string manipulation. C23 adds stricter const rules; code that used to compile cleanly may now produce errors if it implicitly discards const qualifiers. This change ensures that code adheres to const-correctness, preventing accidental modification of immutable data.