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Sat, 26 Dec 2020 01:36:52 -0500 (EST) Subject: Re: [PATCH v3 13/24] Refactor parsing of /proc//smaps To: Luis Machado , gdb-patches@sourceware.org References: <20201109170435.15766-1-luis.machado@linaro.org> <20201109170435.15766-14-luis.machado@linaro.org> Message-ID: Date: Sat, 26 Dec 2020 01:36:52 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20201109170435.15766-14-luis.machado@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Poly-FromMTA: (simark.ca [158.69.221.121]) at Sat, 26 Dec 2020 06:36:52 +0000 X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Simon Marchi via Gdb-patches Reply-To: Simon Marchi Cc: david.spickett@linaro.org Errors-To: gdb-patches-bounces@sourceware.org Sender: "Gdb-patches" On 2020-11-09 12:04 p.m., Luis Machado via Gdb-patches wrote: > The Linux kernel exposes the information about MTE-protected pages via the > proc filesystem, more specifically through the smaps file. > > What we're looking for is a mapping with the 'mt' flag, which tells us that > mapping was created with a PROT_MTE flag and, thus, is capable of using memory > tagging. > > We already parse that file for other purposes (core file > generation/filtering), so this patch refactors the code to make the parsing > of the smaps file reusable for memory tagging. > > The function linux_address_in_memtag_page uses the refactored code to allow > querying for memory tag support in a particular address, and it gets used in the > next patch. > > gdb/ChangeLog: > > YYYY-MM-DD Luis Machado > > * linux-tdep.c (struct smaps_vmflags) : New flag > bit. > (struct smaps_data): New struct. > (decode_vmflags): Handle the 'mt' flag. > (parse_smaps_data): New function, refactored from > linux_find_memory_regions_full. > (linux_address_in_memtag_page): New function. > (linux_find_memory_regions_full): Refactor into parse_smaps_data. > * linux-tdep.h (linux_address_in_memtag_page): New prototype. > --- > gdb/linux-tdep.c | 358 +++++++++++++++++++++++++++++++---------------- > gdb/linux-tdep.h | 4 + > 2 files changed, 241 insertions(+), 121 deletions(-) > > diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c > index bacb61398f..91bdcc133b 100644 > --- a/gdb/linux-tdep.c > +++ b/gdb/linux-tdep.c > @@ -86,8 +86,33 @@ struct smaps_vmflags > /* Is this a MAP_SHARED mapping (VM_SHARED, "sh"). */ > > unsigned int shared_mapping : 1; > + > + /* Memory map has memory tagging enabled. */ > + > + unsigned int memory_tagging : 1; > }; > > +/* Data structure that holds the information contained in the > + /proc//smaps file. */ > + > +struct smaps_data > +{ > + ULONGEST start_address; > + ULONGEST end_address; > + std::string filename; > + struct smaps_vmflags vmflags; > + bool read; > + bool write; > + bool exec; > + bool priv; > + bool has_anonymous; > + bool mapping_anon_p; > + bool mapping_file_p; > + > + ULONGEST inode; > + ULONGEST offset; > +}; > + > /* Whether to take the /proc/PID/coredump_filter into account when > generating a corefile. */ > > @@ -472,6 +497,8 @@ decode_vmflags (char *p, struct smaps_vmflags *v) > v->exclude_coredump = 1; > else if (strcmp (s, "sh") == 0) > v->shared_mapping = 1; > + else if (strcmp (s, "mt") == 0) > + v->memory_tagging = 1; > } > } > > @@ -1267,6 +1294,184 @@ typedef int linux_dump_mapping_p_ftype (filter_flags filterflags, > const char *filename, > ULONGEST addr, > ULONGEST offset); > +/* Helper function to parse the contents of /proc//smaps into a data > + structure, for easy access. > + > + DATA is the contents of the smaps file. The parsed contents are stored > + into the SMAPS vector. */ Add a blank line above this comment. > + > +static int > +parse_smaps_data (const char *data, > + std::vector &smaps, > + const char *mapsfilename) The return value of that function is unused, it always return 0. I'd suggest making it return the std::vector directly. > +{ > + char *line, *t; > + > + gdb_assert (data != nullptr); > + > + smaps.clear (); > + > + line = strtok_r ((char *) data, "\n", &t); > + > + while (line != NULL) > + { > + ULONGEST addr, endaddr, offset, inode; > + const char *permissions, *device, *filename; > + struct smaps_vmflags v; > + size_t permissions_len, device_len; > + int read, write, exec, priv; > + int has_anonymous = 0; > + int mapping_anon_p; > + int mapping_file_p; > + > + memset (&v, 0, sizeof (v)); > + read_mapping (line, &addr, &endaddr, &permissions, &permissions_len, > + &offset, &device, &device_len, &inode, &filename); > + mapping_anon_p = mapping_is_anonymous_p (filename); > + /* If the mapping is not anonymous, then we can consider it > + to be file-backed. These two states (anonymous or > + file-backed) seem to be exclusive, but they can actually > + coexist. For example, if a file-backed mapping has > + "Anonymous:" pages (see more below), then the Linux > + kernel will dump this mapping when the user specified > + that she only wants anonymous mappings in the corefile > + (*even* when she explicitly disabled the dumping of > + file-backed mappings). */ > + mapping_file_p = !mapping_anon_p; > + > + /* Decode permissions. */ > + read = (memchr (permissions, 'r', permissions_len) != 0); > + write = (memchr (permissions, 'w', permissions_len) != 0); > + exec = (memchr (permissions, 'x', permissions_len) != 0); > + /* 'private' here actually means VM_MAYSHARE, and not > + VM_SHARED. In order to know if a mapping is really > + private or not, we must check the flag "sh" in the > + VmFlags field. This is done by decode_vmflags. However, > + if we are using a Linux kernel released before the commit > + 834f82e2aa9a8ede94b17b656329f850c1471514 (3.10), we will > + not have the VmFlags there. In this case, there is > + really no way to know if we are dealing with VM_SHARED, > + so we just assume that VM_MAYSHARE is enough. */ > + priv = memchr (permissions, 'p', permissions_len) != 0; > + > + /* Try to detect if region should be dumped by parsing smaps > + counters. */ > + for (line = strtok_r (NULL, "\n", &t); > + line != NULL && line[0] >= 'A' && line[0] <= 'Z'; > + line = strtok_r (NULL, "\n", &t)) > + { > + char keyword[64 + 1]; > + > + if (sscanf (line, "%64s", keyword) != 1) > + { > + warning (_("Error parsing {s,}maps file '%s'"), mapsfilename); > + break; > + } > + > + if (strcmp (keyword, "Anonymous:") == 0) > + { > + /* Older Linux kernels did not support the > + "Anonymous:" counter. Check it here. */ > + has_anonymous = 1; > + } > + else if (strcmp (keyword, "VmFlags:") == 0) > + decode_vmflags (line, &v); > + > + if (strcmp (keyword, "AnonHugePages:") == 0 > + || strcmp (keyword, "Anonymous:") == 0) > + { > + unsigned long number; > + > + if (sscanf (line, "%*s%lu", &number) != 1) > + { > + warning (_("Error parsing {s,}maps file '%s' number"), > + mapsfilename); > + break; > + } > + if (number > 0) > + { > + /* Even if we are dealing with a file-backed > + mapping, if it contains anonymous pages we > + consider it to be *also* an anonymous > + mapping, because this is what the Linux > + kernel does: > + > + // Dump segments that have been written to. > + if (vma->anon_vma && FILTER(ANON_PRIVATE)) > + goto whole; > + > + Note that if the mapping is already marked as > + file-backed (i.e., mapping_file_p is > + non-zero), then this is a special case, and > + this mapping will be dumped either when the > + user wants to dump file-backed *or* anonymous > + mappings. */ > + mapping_anon_p = 1; > + } > + } > + } > + /* Save the smaps entry to the vector. */ > + struct smaps_data map; > + std::string fname (filename); You don't need to create the string here, just do map.filename = filename; below. > + > + smaps.emplace_back (map); > + } > + > + return 0; > +} > + > +/* See linux-tdep.h. */ > + > +bool > +linux_address_in_memtag_page (CORE_ADDR address) > +{ > + if (current_inferior ()->fake_pid_p) > + return false;> + > + pid_t pid = current_inferior ()->pid; > + > + std::string smaps_file = string_printf ("/proc/%d/smaps", pid); > + > + gdb::unique_xmalloc_ptr data > + = target_fileio_read_stralloc (NULL, smaps_file.c_str ()); > + > + if (data == nullptr) > + return false; > + > + std::vector smaps; > + > + /* Parse the contents of smaps into a vector. */ > + parse_smaps_data (data.get (), smaps, smaps_file.c_str ()); > + > + if (!smaps.empty ()) > + { No need for this `if`. > + for (struct smaps_data map : smaps) Iterate by const reference: for (const smaps_data &map : smaps) > + { > + /* Is the address within [start_address, end_address) in a page > + mapped with memory tagging? */ > + if (address >= map.start_address > + && address < map.end_address > + && map.vmflags.memory_tagging) > + return true; > + } > + } > + > + return false; > +} > > /* List memory regions in the inferior for a corefile. */ > > @@ -1276,8 +1481,7 @@ linux_find_memory_regions_full (struct gdbarch *gdbarch, > linux_find_memory_region_ftype *func, > void *obfd) > { > - char mapsfilename[100]; > - char coredumpfilter_name[100]; > + std::string coredumpfilter_name; Declare this on first use (we could push some preparatory patches to change these to std::string, to make this patch simpler). > pid_t pid; > /* Default dump behavior of coredump_filter (0x33), according to > Documentation/filesystems/proc.txt from the Linux kernel > @@ -1295,10 +1499,9 @@ linux_find_memory_regions_full (struct gdbarch *gdbarch, > > if (use_coredump_filter) > { > - xsnprintf (coredumpfilter_name, sizeof (coredumpfilter_name), > - "/proc/%d/coredump_filter", pid); > + coredumpfilter_name = string_printf ("/proc/%d/coredump_filter", pid); > gdb::unique_xmalloc_ptr coredumpfilterdata > - = target_fileio_read_stralloc (NULL, coredumpfilter_name); > + = target_fileio_read_stralloc (NULL, coredumpfilter_name.c_str ()); > if (coredumpfilterdata != NULL) > { > unsigned int flags; > @@ -1308,125 +1511,39 @@ linux_find_memory_regions_full (struct gdbarch *gdbarch, > } > } > > - xsnprintf (mapsfilename, sizeof mapsfilename, "/proc/%d/smaps", pid); > + std::string mapsfilename = string_printf ("/proc/%d/smaps", pid); > gdb::unique_xmalloc_ptr data > - = target_fileio_read_stralloc (NULL, mapsfilename); > + = target_fileio_read_stralloc (NULL, mapsfilename.c_str ()); > if (data == NULL) > { > /* Older Linux kernels did not support /proc/PID/smaps. */ > - xsnprintf (mapsfilename, sizeof mapsfilename, "/proc/%d/maps", pid); > - data = target_fileio_read_stralloc (NULL, mapsfilename); > + mapsfilename = string_printf ("/proc/%d/maps", pid); > + data = target_fileio_read_stralloc (NULL, mapsfilename.c_str ()); > } > > - if (data != NULL) > - { > - char *line, *t; > - > - line = strtok_r (data.get (), "\n", &t); > - while (line != NULL) > - { > - ULONGEST addr, endaddr, offset, inode; > - const char *permissions, *device, *filename; > - struct smaps_vmflags v; > - size_t permissions_len, device_len; > - int read, write, exec, priv; > - int has_anonymous = 0; > - int should_dump_p = 0; > - int mapping_anon_p; > - int mapping_file_p; > - > - memset (&v, 0, sizeof (v)); > - read_mapping (line, &addr, &endaddr, &permissions, &permissions_len, > - &offset, &device, &device_len, &inode, &filename); > - mapping_anon_p = mapping_is_anonymous_p (filename); > - /* If the mapping is not anonymous, then we can consider it > - to be file-backed. These two states (anonymous or > - file-backed) seem to be exclusive, but they can actually > - coexist. For example, if a file-backed mapping has > - "Anonymous:" pages (see more below), then the Linux > - kernel will dump this mapping when the user specified > - that she only wants anonymous mappings in the corefile > - (*even* when she explicitly disabled the dumping of > - file-backed mappings). */ > - mapping_file_p = !mapping_anon_p; > - > - /* Decode permissions. */ > - read = (memchr (permissions, 'r', permissions_len) != 0); > - write = (memchr (permissions, 'w', permissions_len) != 0); > - exec = (memchr (permissions, 'x', permissions_len) != 0); > - /* 'private' here actually means VM_MAYSHARE, and not > - VM_SHARED. In order to know if a mapping is really > - private or not, we must check the flag "sh" in the > - VmFlags field. This is done by decode_vmflags. However, > - if we are using a Linux kernel released before the commit > - 834f82e2aa9a8ede94b17b656329f850c1471514 (3.10), we will > - not have the VmFlags there. In this case, there is > - really no way to know if we are dealing with VM_SHARED, > - so we just assume that VM_MAYSHARE is enough. */ > - priv = memchr (permissions, 'p', permissions_len) != 0; > - > - /* Try to detect if region should be dumped by parsing smaps > - counters. */ > - for (line = strtok_r (NULL, "\n", &t); > - line != NULL && line[0] >= 'A' && line[0] <= 'Z'; > - line = strtok_r (NULL, "\n", &t)) > - { > - char keyword[64 + 1]; > + if (data == nullptr) > + return 1; > > - if (sscanf (line, "%64s", keyword) != 1) > - { > - warning (_("Error parsing {s,}maps file '%s'"), mapsfilename); > - break; > - } > + std::vector smaps; > > - if (strcmp (keyword, "Anonymous:") == 0) > - { > - /* Older Linux kernels did not support the > - "Anonymous:" counter. Check it here. */ > - has_anonymous = 1; > - } > - else if (strcmp (keyword, "VmFlags:") == 0) > - decode_vmflags (line, &v); > + /* Parse the contents of smaps into a vector. */ > + parse_smaps_data (data.get (), smaps, mapsfilename.c_str ()); > > - if (strcmp (keyword, "AnonHugePages:") == 0 > - || strcmp (keyword, "Anonymous:") == 0) > - { > - unsigned long number; > - > - if (sscanf (line, "%*s%lu", &number) != 1) > - { > - warning (_("Error parsing {s,}maps file '%s' number"), > - mapsfilename); > - break; > - } > - if (number > 0) > - { > - /* Even if we are dealing with a file-backed > - mapping, if it contains anonymous pages we > - consider it to be *also* an anonymous > - mapping, because this is what the Linux > - kernel does: > - > - // Dump segments that have been written to. > - if (vma->anon_vma && FILTER(ANON_PRIVATE)) > - goto whole; > - > - Note that if the mapping is already marked as > - file-backed (i.e., mapping_file_p is > - non-zero), then this is a special case, and > - this mapping will be dumped either when the > - user wants to dump file-backed *or* anonymous > - mappings. */ > - mapping_anon_p = 1; > - } > - } > - } > + if (!smaps.empty ()) > + { > + for (struct smaps_data map : smaps) Same comments as above. Simon