On 11/02/26 10:59, Frédéric Bérat wrote:
> Adds support for excluding specific categories from `LD_DEBUG` output.
>
> The `LD_DEBUG` environment variable now accepts category names prefixed
> with a dash (`-`) to disable their debugging output. This allows users
> to enable broad categories (e.g., `all`) while suppressing verbose or
> irrelevant information from specific sub-categories (e.g., `-tls`).
>
> The `process_dl_debug` function in `rtld.c` has been updated to parse
> these exclusion options and unset the corresponding bits in
> `GLRO(dl_debug_mask)`. The `LD_DEBUG=help` output has also been updated
> to document this new functionality. A new test `tst-dl-debug-exclude.sh`
> is added to verify the correct behavior of category exclusion.
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> v4:
> - Refactor parsing to process options sequentially in a single loop.
> - Ensure the last specified option for a category takes precedence
> (fixing ordering).
> - Update tst-dl-debug-exclude.sh to verify sequential processing and
> ordering (e.g., -tls,tls).
> - Improve script header and intent description.
>
> elf/Makefile | 11 +++++
> elf/rtld.c | 16 +++++--
> elf/tst-dl-debug-exclude.sh | 87 +++++++++++++++++++++++++++++++++++++
> 3 files changed, 110 insertions(+), 4 deletions(-)
> create mode 100644 elf/tst-dl-debug-exclude.sh
>
> diff --git a/elf/Makefile b/elf/Makefile
> index 9d4dfcf4ae..f6822dc379 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -3553,4 +3553,15 @@ $(objpfx)tst-tls-debug-recursive.out: tst-tls-debug-recursive.sh \
> '$(rtld-prefix)' '$(run_program_env)' \
> $(objpfx)tst-recursive-tls > $@; \
> $(evaluate-test)
> +
> +tests-special += $(objpfx)tst-dl-debug-exclude.out
> +$(objpfx)tst-dl-debug-exclude.out: tst-dl-debug-exclude.sh \
> + $(objpfx)tst-recursive-tls \
> + $(objpfx)tst-recursive-tlsmallocmod.so \
> + $(patsubst %,$(objpfx)tst-recursive-tlsmod%.so, \
> + 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15)
> + $(SHELL) $< $(common-objpfx) '$(test-wrapper-env)' \
> + '$(rtld-prefix)' '$(run_program_env)' \
> + $(objpfx)tst-recursive-tls > $@; \
> + $(evaluate-test)
> endif
> diff --git a/elf/rtld.c b/elf/rtld.c
> index 1fc32ebefa..e1c2105ba6 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -2461,11 +2461,18 @@ process_dl_debug (struct dl_main_state *state, const char *dl_debug)
> && dl_debug[len] != ',' && dl_debug[len] != ':')
> ++len;
>
> + bool exclude = *dl_debug == '-';
> + const char *name = exclude ? dl_debug + 1 : dl_debug;
> + size_t name_len = exclude ? len - 1 : len;
> +
> for (cnt = 0; cnt < ndebopts; ++cnt)
> - if (debopts[cnt].len == len
> - && memcmp (dl_debug, debopts[cnt].name, len) == 0)
> + if (debopts[cnt].len == name_len
> + && memcmp (name, debopts[cnt].name, name_len) == 0)
> {
> - GLRO(dl_debug_mask) |= debopts[cnt].mask;
> + if (exclude)
> + GLRO(dl_debug_mask) &= ~debopts[cnt].mask;
> + else
> + GLRO(dl_debug_mask) |= debopts[cnt].mask;
> break;
> }
>
> @@ -2507,7 +2514,8 @@ Valid options for the LD_DEBUG environment variable are:\n\n");
>
> _dl_printf ("\n\
> To direct the debugging output into a file instead of standard output\n\
> -a filename can be specified using the LD_DEBUG_OUTPUT environment variable.\n");
> +a filename can be specified using the LD_DEBUG_OUTPUT environment variable.\n\
> +Categories can be excluded by prefixing them with a dash (-).\n");
> _exit (0);
> }
> }
> diff --git a/elf/tst-dl-debug-exclude.sh b/elf/tst-dl-debug-exclude.sh
> new file mode 100644
> index 0000000000..9837ffcea8
> --- /dev/null
> +++ b/elf/tst-dl-debug-exclude.sh
> @@ -0,0 +1,87 @@
> +#!/bin/sh
> +# Test for LD_DEBUG category exclusion.
> +# Copyright (C) 2026 Free Software Foundation, Inc.
> +# This file is part of the GNU C Library.
> +#
> +# The GNU C Library is free software; you can redistribute it and/or
> +# modify it under the terms of the GNU Lesser General Public
> +# License as published by the Free Software Foundation; either
> +# version 2.1 of the License, or (at your option) any later version.
> +#
> +# The GNU C Library is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> +# Lesser General Public License for more details.
> +#
> +# You should have received a copy of the GNU Lesser General Public
> +# License along with the GNU C Library; if not, see
> +# <https://www.gnu.org/licenses/>.
> +
> +# This script verifies the LD_DEBUG category exclusion functionality.
> +# It checks that:
> +# 1. Categories can be excluded using the '-' prefix.
> +# 2. Options are processed sequentially, meaning the last specified
> +# option for a category (enable or exclude) takes precedence.
> +
> +set -e
> +
> +common_objpfx="$1"
> +test_wrapper_env="$2"
> +rtld_prefix="$3"
> +run_program_env="$4"
> +test_program="$5"
> +
> +debug_output="${common_objpfx}elf/tst-dl-debug-exclude.debug"
> +rm -f "${debug_output}".*
> +
> +# Run the test program with LD_DEBUG=all,-tls.
> +# We expect general logs but no TLS logs.
> +eval "${test_wrapper_env}" LD_DEBUG=all,-tls LD_DEBUG_OUTPUT="${debug_output}" \
> + "${rtld_prefix}" "${test_program}"
> +
> +fail=0
> +
> +# 1. Check that general logs are present (e.g., file loading)
> +if ! grep -q 'file=' "${debug_output}".*; then
> + echo "FAIL: 'file=' message not found (LD_DEBUG=all failed)"
> + fail=1
> +fi
> +
> +# 2. Check that TLS logs are NOT present
> +if grep -q 'tls: ' "${debug_output}".*; then
> + echo "FAIL: TLS message found (exclusion of -tls failed)"
> + fail=1
> +fi
> +
> +rm -f "${debug_output}".*
> +# 3. Check for LD_DEBUG=all,-tls,tls (ordering verification)
> +# We expect TLS logs to BE present
> +eval "${test_wrapper_env}" LD_DEBUG=all,-tls,tls LD_DEBUG_OUTPUT="${debug_output}" \
> + "${rtld_prefix}" "${test_program}"
> +
> +if ! grep -q 'tls: ' "${debug_output}".*; then
> + echo "FAIL: TLS message not found (ordering -tls,tls failed)"
> + fail=1
> +fi
> +
> +rm -f "${debug_output}".*
> +# 4. Check for LD_DEBUG=tls,-tls
> +# We expect TLS logs to NOT be present
> +eval "${test_wrapper_env}" LD_DEBUG=tls,-tls LD_DEBUG_OUTPUT="${debug_output}" \
> + "${rtld_prefix}" "${test_program}"
> +
> +if grep -q 'tls: ' "${debug_output}".*; then
> + echo "FAIL: TLS message found (ordering tls,-tls failed)"
> + fail=1
> +fi
> +
> +if [ $fail -ne 0 ]; then
> + echo "Test FAILED"
> + cat "${debug_output}".*
> + rm -f "${debug_output}".*
> + exit 1
> +fi
> +
> +echo "Test PASSED"
> +rm -f "${debug_output}".*
> +exit 0