[RFC PATCH v6 20/34] dyndbg: RFC handle __dyndbg* sections in module.lds.h

Jim Cromie
2021-05-29T20:03:07Z

Up until now, loadable modules have tacitly linked the 2 __dyndbg*
sections into the .ko, as observable in log by enabling module.c's
pr_debugs and loading a module.

But now, we need to explicitly compose our named output sections,
placing the header sections in front of their respective __dyndbg*
input sections. We reuse input section names for the output.

This gives us the placement we need for the header record, which we
can see in the "add-module:"s and elements "0 0" below:

"0 0" lines are headers: predicate (function==module && !lineno)
"X debug prints in" are 1 too high, they count headers.
we are adding tables for empty modules (1st 2 below)

[ 7.578873] dyndbg: add-module: ghash_clmulni_intel
[ 7.579716] dyndbg: 0 0 ghash_clmulni_intel.ghash_clmulni_intel.0
[ 7.608995] dyndbg: 1 debug prints in module ghash_clmulni_intel
[ 8.078085] dyndbg: add-module: rapl
[ 8.078977] dyndbg: 0 0 rapl.rapl.0
[ 8.079584] dyndbg: 1 debug prints in module rapl
[ 8.082009] RAPL PMU: API unit is 2^-32 Joules, 0 fixed counters, 10737418240 ms ovfl timer
[ 8.099294] dyndbg: add-module: intel_rapl_common
[ 8.100177] dyndbg: 0 0 intel_rapl_common.intel_rapl_common.0
[ 8.101026] dyndbg: 1 1 intel_rapl_common.rapl_remove_package.1279
[ 8.101931] dyndbg: 2 2 intel_rapl_common.rapl_detect_domains.1245
[ 8.102836] dyndbg: 3 3 intel_rapl_common.rapl_detect_domains.1242
[ 8.103778] dyndbg: 4 4 intel_rapl_common.rapl_package_register_powercap.1159
[ 8.104960] dyndbg: 5 5 intel_rapl_common.rapl_package_register_powercap.1145
[ 8.106246] dyndbg: 6 6 intel_rapl_common.rapl_package_register_powercap.1114
[ 8.107302] dyndbg: 7 7 intel_rapl_common.rapl_package_register_powercap.1108
[ 8.108338] dyndbg: 8 8 intel_rapl_common.rapl_update_domain_data.1083
[ 8.109278] dyndbg: 9 9 intel_rapl_common.rapl_check_unit_atom.824
[ 8.110255] dyndbg: 10 10 intel_rapl_common.rapl_check_unit_core.796
[ 8.111361] dyndbg: 11 11 intel_rapl_common.rapl_read_data_raw.722
[ 8.112301] dyndbg: 12 12 intel_rapl_common.contraint_to_pl.303
[ 8.113276] dyndbg: 13 debug prints in module intel_rapl_common
[ 8.130452] dyndbg: add-module: intel_rapl_msr
[ 8.131140] dyndbg: 0 0 intel_rapl_msr.intel_rapl_msr.0
[ 8.132026] dyndbg: 1 1 intel_rapl_msr.rapl_msr_probe.172
[ 8.132818] dyndbg: 2 2 intel_rapl_msr.rapl_msr_read_raw.104
[ 8.133794] dyndbg: 3 debug prints in module intel_rapl_msr

This gives us the property we need:

fixed offset from &__dyndbg[N] to &__dyndbg[0]
container_of gets &header
header has ptr to __dyndbg_sites[]
we can (in principle) drop __dyndbg.site ptr
(after we adapt header to keep it)

TODO:

At this point, for loaded modules, ddebug_add_module() sees the header
as 0'th element, as we need in order to drop site (and regain worst
case footprint parity).

It could/should properly init this header to support the _sites[n]
lookup for loaded mods. Or at least handle it explicitly. Or at
least see what proc-show does with it currently.

Note that for builtins, decided by (__start <= dp < __stop), we use
__start___dyndbg_sites[N] directly, and dont need the header.

But maybe we should use it anyway, double-checking/BUGing when wrong.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
include/asm-generic/module.lds.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/module.lds.h b/include/asm-generic/module.lds.h
index f210d5c1b78b..70e744c953f5 100644
--- a/include/asm-generic/module.lds.h
+++ b/include/asm-generic/module.lds.h
@@ -4,7 +4,14 @@

/*
* <asm/module.lds.h> can specify arch-specific sections for linking modules.
- * Empty for the asm-generic header.
+ *
+ * Normally, sections get thru tacitly, but for CONFIG_DYNAMIC_DEBUG,
+ * we need to insert the .gnu.linkonce sections into the output
+ * sections, so we have to say everything explicitly.
*/
+SECTIONS {
+__dyndbg_sites : ALIGN(8) { *(.gnu.linkonce.dyndbg_site) *(__dyndbg_sites) }
+__dyndbgs : ALIGN(8) { *(.gnu.linkonce.dyndbg) *(__dyndbgs) }
+}

#endif /* __ASM_GENERIC_MODULE_LDS_H */
--
2.31.1