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(c-24-9-77-57.hsd1.co.comcast.net. [24.9.77.57]) by smtp.googlemail.com with ESMTPSA id t39sm1868064ooi.42.2021.05.29.13.02.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 29 May 2021 13:02:32 -0700 (PDT) From: Jim Cromie To: jbaron@akamai.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org Cc: Jim Cromie Subject: [RFC PATCH v6 19/34] dyndbg: RFC - DEFINE_DYNAMIC_DEBUG_TABLE Date: Sat, 29 May 2021 14:00:14 -0600 Message-Id: <20210529200029.205306-20-jim.cromie@gmail.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210529200029.205306-1-jim.cromie@gmail.com> References: <20210529200029.205306-1-jim.cromie@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org DEFINE_DYNAMIC_DEBUG_TABLE is based on DEFINE_DYNAMIC_DEBUG_METADATA. Like its model, it creates/allocates a pair of structs: _ddebug & _ddebug_site. It inits them distinctively, so is_dyndbg_header_pair() macro can verify them. Its purpose is to reserve a single pair of header records in the front of the "__dyndbgs" & "__dyndbg_sites" sections. This has several parts; - the pair of structs are defined in 2 .gnu.linkonce.dyndbg* sections corresponding to the 2 dyndbg* sections populated by _METADATA - vmlinux.lds.h places these 2 new sections into the dyndbg* sections, right after the start___dyndbg*s, before existing contents. - the pair has "__used __weak" to qualm compiler concerns. explicit externs were problematic with initialization, static decls too. With this, the header record is now really __dyndbg[0]. Notes: DYNAMIC_DEBUG is a 'transparent' facility, in that pr_debug() users get extra features without additional api. Because of this, DEFINE_DYNAMIC_DEBUG_TABLE is invoked by dynamic_debug.h on behalf of all its (indirect) users, including printk.h. IOW this has wide effects; it resulted in multiple redundant definitions of header records. By hunch then trial and error, using .gnu.linkonce. sections and "__used __weak " modifiers resolved the problems. RFC. In vmlinux-lds.h, I added 2 more KEEPs to place the .gnu.linkonce.* headers at the front of their respective __dyndbg* sections. I moved the __dyndbg lines into a new macro, which maybe should be done as a separate commit, or in the earlier commit that touched it. The headers are really just struct _ddebug*s, they are initialized distinctively so that they're recogizable by code, using macro is_dyndbg_header_pair(dbg, dbgsite). DECLARE_DYNAMIC_DEBUG_TABLE() initializes the header record pairs with values which are "impossible" for pr_debug()s: (and therefor distinctive) - lineno == 0 - site == iter->site - modname == function not possible in proper linkage - modname == format not possible in normal linkage - filename = (void*) iter forced loopback Next: Get __dyndbg[0] from any *dp within __dyndbg[N]. Then with __dyndbg[0].site, we can get __dyndbg_sites[N]. This is a little slower than a direct pointer, but this is an unlikely debug path, so this 'up-N-over-down-N' access is ok. Eventually we can adapt the header (as a new struct/union) to keep its pointer to the __dyndbg_sites[] section/block, while allowing us to drop it from struct _ddebug, regaining memory parity with master. But for now, we keep .site, and will soon use it to validate the 'up-N-over-down-N' computation. For clarity, N is _ddebug._index. For both builtins & loadable modules, it is init'd to remember the fixed offset from the beginning of the section/block/memory-allocation (actual elf sections for *ko's, and a __start/__stop delineated part of .data for builtins). N/_index will be used solely to get to __debugs[0] and over to __debug_sites[N]. It is distinct from a module's numdbgs, which is used mainly when walking control, and is kept in struct _ddeug_table. Signed-off-by: Jim Cromie --- include/asm-generic/vmlinux.lds.h | 2 ++ include/linux/dynamic_debug.h | 45 +++++++++++++++++++++++++++++++ lib/dynamic_debug.c | 18 ++++++------- 3 files changed, 56 insertions(+), 9 deletions(-) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index f4e861282ed7..11a194fe3cd9 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -340,9 +340,11 @@ #define DYNAMIC_DEBUG_DATA() \ . = ALIGN(8); \ __start___dyndbg_sites = .; \ + KEEP(*(.gnu.linkonce.dyndbg_site)) \ KEEP(*(__dyndbg_sites)) \ __stop___dyndbg_sites = .; \ __start___dyndbg = .; \ + KEEP(*(.gnu.linkonce.dyndbg)) \ KEEP(*(__dyndbgs)) \ __stop___dyndbg = .; #else diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h index c866b4a9760a..a99973221f94 100644 --- a/include/linux/dynamic_debug.h +++ b/include/linux/dynamic_debug.h @@ -113,6 +113,43 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor, _DPRINTK_KEY_INIT \ } +/* + * DEFINE_DYNAMIC_DEBUG_TABLE(): This is a special version of + * DEFINE_DYNAMIC_DEBUG_METADATA(). It creates a single pair of + * header records, which linker scripts place into __dyndbg[0] & + * __dyndbg_sites[0]. + * To allow a robust runtime test for is_dyndbg_header_pair(I,S), + * force-initialize S->filename to point back to I, an otherwize + * pathological condition. + */ +#define DEFINE_DYNAMIC_DEBUG_TABLE() \ + /* forward decl, allowing loopback pointer */ \ + __weak struct _ddebug __used __aligned(8) \ + __section(".gnu.linkonce.dyndbg") \ + _LINKONCE_dyndbg_header; \ + __weak struct _ddebug_site __used __aligned(8) \ + __section(".gnu.linkonce.dyndbg_site") \ + _LINKONCE_dyndbg_site_header = { \ + .modname = KBUILD_MODNAME, \ + .function = KBUILD_MODNAME, \ + /* forced pointer loopback, for distinction */ \ + .filename = (void *) &_LINKONCE_dyndbg_header \ + }; \ + __weak struct _ddebug __used __aligned(8) \ + __section(".gnu.linkonce.dyndbg") \ + _LINKONCE_dyndbg_header = { \ + .site = &_LINKONCE_dyndbg_site_header, \ + .format = KBUILD_MODNAME \ + } + +/* The header initializations as a distinguishing predicate */ +#define is_dyndbg_header_pair(iter, sitep) \ + (sitep == iter->site \ + && (!iter->lineno) \ + && (iter->format == sitep->modname) \ + && (sitep->modname == sitep->function) \ + && ((void *)sitep->filename == (void *)iter)) + #ifdef CONFIG_JUMP_LABEL #ifdef DEBUG @@ -243,4 +280,12 @@ static inline int dynamic_debug_exec_queries(const char *query, const char *modn #endif /* !CONFIG_DYNAMIC_DEBUG_CORE */ +#if ((defined(CONFIG_DYNAMIC_DEBUG) || \ + (defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))) \ + && defined(KBUILD_MODNAME) && !defined(NO_DYNAMIC_DEBUG_TABLE)) + +/* transparently invoked, except when -DNO_DYNAMIC_DEBUG_TABLE */ +DEFINE_DYNAMIC_DEBUG_TABLE(); +#endif + #endif diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c index ce134c939f01..e4a22f7b153f 100644 --- a/lib/dynamic_debug.c +++ b/lib/dynamic_debug.c @@ -1190,8 +1190,7 @@ static int __init dynamic_debug_init(void) const char *modname = NULL; char *cmdline; int ret = 0; - int site_ct = 0, entries = 0, modct = 0; - int mod_index = 0; + int i, site_ct = 0, modct = 0, mod_index = 0; if (&__start___dyndbg == &__stop___dyndbg) { if (IS_ENABLED(CONFIG_DYNAMIC_DEBUG)) { @@ -1207,10 +1206,9 @@ static int __init dynamic_debug_init(void) site = site_mod_start = __start___dyndbg_sites; modname = site->modname; - for (; iter < __stop___dyndbg; iter++, site++) { + for (i = 0; iter < __stop___dyndbg; iter++, site++, i++) { - BUG_ON(site != iter->site); - entries++; + WARN_ON(site != iter->site); if (strcmp(modname, site->modname)) { modct++; @@ -1219,10 +1217,12 @@ static int __init dynamic_debug_init(void) site_ct, mod_index, modname); if (ret) goto out_err; - site_ct = 0; + modname = site->modname; iter_mod_start = iter; site_mod_start = site; + mod_index += site_ct; + site_ct = 0; } site_ct++; } @@ -1232,9 +1232,9 @@ static int __init dynamic_debug_init(void) ddebug_init_success = 1; vpr_info("%d prdebugs in %d modules, %d KiB in ddebug tables, %d KiB in __dyndbg section, %d KiB in __dyndbg_sites section\n", - entries, modct, (int)((modct * sizeof(struct ddebug_table)) >> 10), - (int)((entries * sizeof(struct _ddebug)) >> 10), - (int)((entries * sizeof(struct _ddebug_site)) >> 10)); + i, modct, (int)((modct * sizeof(struct ddebug_table)) >> 10), + (int)((i * sizeof(struct _ddebug)) >> 10), + (int)((i * sizeof(struct _ddebug_site)) >> 10)); /* apply ddebug_query boot param, dont unload tables on err */ if (ddebug_setup_string[0] != '\0') { -- 2.31.1