If it is present, it must precede any loadable segment entry.
.TP
.BR PT_NOTE
-The array element specifies the location and size for auxiliary information.
+The array element specifies the location of notes (ElfN_Nhdr).
.TP
.BR PT_SHLIB
This segment type is reserved but has unspecified semantics.
have only one dynamic section.
.TP
.BR SHT_NOTE
-This section holds information that marks the file in some way.
+This section holds notes (ElfN_Nhdr).
.TP
.BR SHT_NOBITS
A section of this type occupies no space in the file but otherwise
No attribute types are used.
.TP
.IR .note
-This section holds information in the
-"Note Section"
-format.
+This section holds various notes.
This section is of type
.BR SHT_NOTE .
No attribute types are used.
-OpenBSD
-native executables usually contain a
-.I .note.openbsd.ident
-section to identify themselves, for the kernel to bypass any compatibility
-ELF binary emulation tests when loading the file.
+.TP
+.IR .note.ABI-tag
+This section is used to declare the expected runtime ABI of the ELF.
+It may include the operating system name and its runtime versions.
+This section is of type
+.BR SHT_NOTE .
+The only attribute used is
+.BR SHF_ALLOC .
+.TP
+.IR .note.gnu.build-id
+This section is used to hold an ID that uniquely identifies the contents of the
+ELF.
+Different files with the same build ID should contain the same executable
+content.
+See the
+.IR \-\-build\-id
+option to the GNU linker (\fBld\fR (1)) for more details.
+This section is of type
+.BR SHT_NOTE .
+The only attribute used is
+.BR SHF_ALLOC .
.TP
.IR .note.GNU-stack
This section is used in Linux object files for declaring stack attributes.
This indicates to the GNU linker that the object file requires an
executable stack.
.TP
+.IR .note.openbsd.ident
+OpenBSD native executables usually contain this section to identify themselves
+so the kernel can bypass any compatibility ELF binary emulation tests when
+loading the file.
+.TP
.IR .plt
This section holds the procedure linkage table.
This section is of type
.I .dynamic
section.
This is automatically populated by the linker.
+.\" GABI ELF Reference for Note Sections:
+.\" http://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section
+.\"
+.\" Note that it implies the sizes and alignments of notes depend on the ELF
+.\" size (e.g. 32-bit ELFs have three 4-byte words and use 4-byte alignment
+.\" while 64-bit ELFs use 8-byte words & alignment), but that is not the case
+.\" in the real world. Notes always have three 4-byte words as can be seen
+.\" in the source links below (remember that Elf64_Word is a 32-bit quantity).
+.\" glibc: https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/elf.h;h=9e59b3275917549af0cebe1f2de9ded3b7b10bf2#l1173
+.\" binutils: https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=binutils/readelf.c;h=274ddd17266aef6e4ad1f67af8a13a21500ff2af#l15943
+.\" Linux: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/elf.h?h=v4.8#n422
+.\" Solaris: https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-18048.html
+.\" FreeBSD: https://svnweb.freebsd.org/base/head/sys/sys/elf_common.h?revision=303677&view=markup#l33
+.\" NetBSD: https://www.netbsd.org/docs/kernel/elf-notes.html
+.\" OpenBSD: https://github.com/openbsd/src/blob/master/sys/sys/exec_elf.h#L533
+.SS Notes (Nhdr)
+ELF notes allow for appending arbitrary information for the system to use.
+They are largely used by core files (\fIe_type\fR of \fIET_CORE\fR),
+but many projects define their own set of extensions.
+For example, the GNU project passes info from the linker to the C library.
+
+Note sections contain a series of notes (see the structs below).
+Each note is followed by the name field (whose length is defined in
+\fIn_namesz\fR) and then by the descriptor field (whose length is defined in
+\fIn_descsz\fR) and whose starting address has a 4 byte alignment.
+Neither field is defined in the note struct due to their arbitrary lengths.
+
+An example for parsing out two consecutive notes should clarify their layout
+in memory.
+
+.in +4n
+.nf
+void *memory, *name, *desc;
+Elf64_Nhdr *note, *next_note;
+
+/* The buffer is pointing to the start of the section/segment. */
+note = memory;
+/* If the name is defined, it follows the note. */
+name = note->n_namesz == 0 ? NULL : memory + sizeof(*note);
+/* If the descriptor is defined, it follows the name (with alignment). */
+desc = note->n_descsz == 0 ? NULL :
+ memory + sizeof(*note) + ALIGN_UP(note->n_namesz, 4);
+/* The next note follows both (with alignment). */
+next_note = memory + sizeof(*note) +
+ ALIGN_UP(note->n_namesz, 4) + ALIGN_UP(note->n_descsz, 4);
+.fi
+.in
+
+Keep in mind that the interpretation of
+.I n_type
+depends on the namespace defined by the
+.I n_namesz
+field.
+After, of course, whether the ELF image has been determined to be a core.
+.in +4n
+.nf
+
+typedef struct {
+ Elf32_Word n_namesz;
+ Elf32_Word n_descsz;
+ Elf32_Word n_type;
+} Elf32_Nhdr;
+.fi
+.in
+.in +4n
+.nf
+
+typedef struct {
+ Elf64_Word n_namesz;
+ Elf64_Word n_descsz;
+ Elf64_Word n_type;
+} Elf64_Nhdr;
+.fi
+.in
+.TP \n[l1_indent]
+.IR n_namesz
+The length of the name field in bytes.
+The contents will immediately follow this note in memory.
+The name is null terminated.
+For example, if the name is "GNU", then
+.I n_namesz
+will be set to 4.
+.TP
+.IR n_descsz
+The length of the descriptor field in bytes.
+The contents will immediately follow the name field in memory.
+.TP
+.IR n_type
+Depending on the value of the name field, this member may have any of the
+following values:
+.RS \n[l1_indent]
+.TP 5
+.B Core files (e_type = ET_CORE)
+Notes used by all core files.
+These are highly operating system or architecture specific and often require
+close coordination with kernels, C libraries, and debuggers.
+.RS
+.TP 21
+.PD 0
+.B NT_PRSTATUS
+prstatus struct
+.TP
+.B NT_FPREGSET
+fpregset struct
+.TP
+.B NT_PRPSINFO
+prpsinfo struct
+.TP
+.B NT_PRXREG
+prxregset struct
+.TP
+.B NT_TASKSTRUCT
+task structure
+.TP
+.B NT_PLATFORM
+String from sysinfo(SI_PLATFORM)
+.TP
+.B NT_AUXV
+auxv array
+.TP
+.B NT_GWINDOWS
+gwindows struct
+.TP
+.B NT_ASRS
+asrset struct
+.TP
+.B NT_PSTATUS
+pstatus struct
+.TP
+.B NT_PSINFO
+psinfo struct
+.TP
+.B NT_PRCRED
+prcred struct
+.TP
+.B NT_UTSNAME
+utsname struct
+.TP
+.B NT_LWPSTATUS
+lwpstatus struct
+.TP
+.B NT_LWPSINFO
+lwpinfo struct
+.TP
+.B NT_PRFPXREG
+fprxregset struct
+.TP
+.B NT_SIGINFO
+siginfo_t (size might increase over time)
+.TP
+.B NT_FILE
+Contains information about mapped files
+.TP
+.B NT_PRXFPREG
+user_fxsr_struct
+.TP
+.B NT_PPC_VMX
+PowerPC Altivec/VMX registers
+.TP
+.B NT_PPC_SPE
+PowerPC SPE/EVR registers
+.TP
+.B NT_PPC_VSX
+PowerPC VSX registers
+.TP
+.B NT_386_TLS
+i386 TLS slots (struct user_desc)
+.TP
+.B NT_386_IOPERM
+x86 io permission bitmap (1=deny)
+.TP
+.B NT_X86_XSTATE
+x86 extended state using xsave
+.TP
+.B NT_S390_HIGH_GPRS
+s390 upper register halves
+.TP
+.B NT_S390_TIMER
+s390 timer register
+.TP
+.B NT_S390_TODCMP
+s390 time-of-day (TOD) clock comparator register
+.TP
+.B NT_S390_TODPREG
+s390 time-of-day (TOD) programmable register
+.TP
+.B NT_S390_CTRS
+s390 control registers
+.TP
+.B NT_S390_PREFIX
+s390 prefix register
+.TP
+.B NT_S390_LAST_BREAK
+s390 breaking event address
+.TP
+.B NT_S390_SYSTEM_CALL
+s390 system call restart data
+.TP
+.B NT_S390_TDB
+s390 transaction diagnostic block
+.TP
+.B NT_ARM_VFP
+ARM VFP/NEON registers
+.TP
+.B NT_ARM_TLS
+ARM TLS register
+.TP
+.B NT_ARM_HW_BREAK
+ARM hardware breakpoint registers
+.TP
+.B NT_ARM_HW_WATCH
+ARM hardware watchpoint registers
+.TP
+.B NT_ARM_SYSTEM_CALL
+ARM system call number
+.PD
+.RE
+
+.TP
+.B n_name = GNU
+Extensions used by the GNU tool chain.
+.RS
+.TP 21
+.PD 0
+.B NT_GNU_ABI_TAG
+OS ABI information.
+The desc field will be 4 words:
+ word 0: OS descriptor (\fBELF_NOTE_OS_LINUX\fR, \fBELF_NOTE_OS_GNU\fR, etc...)
+ word 1: major version of the ABI
+ word 2: minor version of the ABI
+ word 3: subminor version of the ABI
+.TP
+.B NT_GNU_HWCAP
+Synthetic hwcap information.
+The desc field begins with two words:
+ word 0: number of entries
+ word 1: bitmask of enabled entries
+.br
+Then follow variable-length entries, one byte followed by a null-terminated
+hwcap name string.
+The byte gives the bit number to test if enabled, (1U << bit) & bitmask.
+.TP
+.B NT_GNU_BUILD_ID
+Unique build ID as generated by GNU ld's \fI--build-id\fR.
+The desc consists of any nonzero number of bytes.
+.TP
+.B NT_GNU_GOLD_VERSION
+The desc contains the GNU Gold linker version used.
+.PD
+.RE
+
+.TP
+.B Unknown system
+The fallback set of note types when the namespace is unknown.
+Usually the name field will be omitted (i.e.
+.B n_namesz
+will be set to 0).
+.RS
+.TP 21
+.PD 0
+.B NT_VERSION
+A version string of some sort.
+.TP
+.B NT_ARCH
+Architecture information.
+.PD
+.RE
+
+.RE
.SH NOTES
.\" OpenBSD
.\" ELF support first appeared in
projects / thirdparty / man-pages.git / commitdiff
