Date: Fri, 8 Dec 2023 21:57:49 GMT From: Gordon Bergling <gbe@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 914cb28ba291 - stable/13 - Document library types in the intro(3) manual page Message-ID: <202312082157.3B8LvnVp003899@gitrepo.freebsd.org>
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The branch stable/13 has been updated by gbe: URL: https://cgit.FreeBSD.org/src/commit/?id=914cb28ba29175552d7afab4a2e0f1af59e21e8f commit 914cb28ba29175552d7afab4a2e0f1af59e21e8f Author: Gordon Bergling <gbe@FreeBSD.org> AuthorDate: 2023-11-16 09:48:09 +0000 Commit: Gordon Bergling <gbe@FreeBSD.org> CommitDate: 2023-12-08 21:57:32 +0000 Document library types in the intro(3) manual page Add a paragraph about library types to the intro(3) manual page. Document library types, locations and versioning. Reviewed by: emaste, jilles, mhorne, pauamma_gundo.com Obtained from: OpenBSD (partial) Differential Revision: https://reviews.freebsd.org/D36594 (cherry picked from commit 54611b7cc69cee34e7bcdc2324a9159e7543a125) --- share/man/man3/intro.3 | 97 ++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 94 insertions(+), 3 deletions(-) diff --git a/share/man/man3/intro.3 b/share/man/man3/intro.3 index c36ab620bed3..bfae9093af93 100644 --- a/share/man/man3/intro.3 +++ b/share/man/man3/intro.3 @@ -26,8 +26,7 @@ .\" SUCH DAMAGE. .\" .\" @(#)intro.3 8.1 (Berkeley) 6/5/93 -.\" -.Dd November 7, 2022 +.Dd November 16, 2023 .Dt INTRO 3 .Os .Sh NAME @@ -278,13 +277,105 @@ the math library .It Pa /usr/lib/libm_p.a the math library compiled for profiling .El +.Sh LIBRARY TYPES +The system libraries are located in +.Pa /lib +and +.Pa /usr/lib . +A library has the following naming convention: +.Bd -unfilled -offset indent +libc.so.7 +.Ed +.Pp +Libraries with an +.Sq .a +suffix are static. +When a program is linked against a static library, all necessary library code +will be included in the binary. +This means the binary can be run even when the libraries are unavailable. +However, it can be inefficient with both disk space and memory usage +during execution. +The C compiler, +.Xr cc 1 , +can be instructed to link statically by specifying the +.Fl static +flag. +.Pp +Libraries with a +.Sq .so.X +suffix are dynamic libraries. +When code is linked dynamically, the library code that the application needs +is not included in the binary. +Instead, data structures are added containing information about which dynamic +libraries to link with. +When the binary is executed, the run-time linker +.Xr ld.so 1 +reads these data structures and loads them into the +process virtual address space. +.Xr rtld 1 +loads the shared libraries when the program is executed. +.Pp +.Sq X +represents the library version number of the library. +In the example above, a binary linked with +.Pa libc.so.8 +would not be usable on a system where only +.Pa libc.so.7 +is available. +.Pp +The advantages of dynamic libraries are that multiple instances of the same +library can share address space, and the physical size of the binary is +smaller. +A namespace per shared library is available via hidden visibility, +allowing multiple compilation units in a library to share things without +making them available to other libraries. +It is possible to load libraries dynamically via +.Xr dlopen 3 . +The disadvantage is the added complexity that comes with loading the +libraries dynamically, and the extra time taken to load the libraries. +Of course, if the libraries are not available, the binary will be unable +to execute. +Calls across shared libraries are also slightly slower and cannot be +inlined, not even with link time optimization. +The C compiler, +.Xr cc 1 , +can be instructed to link dynamically by specifying the +.Fl shared +flag. +.Pp +Shared libraries, as well as static libraries on architectures which produce +position-independent executables +.Pq PIEs +by default, contain position-independent code +.Pq PIC . +Normally, compilers produce relocatable code. +Relocatable code needs to be modified at run-time, depending on where in +memory it is to be run. +The C compiler, +.Xr cc 1 , +can be instructed to generate PIC code by specifying the +.Fl fPIC +flag. +.Pp +Static libraries are generated using the +.Xr ar 1 +utility. +The libraries contain an index to the contents of the library, +stored within the library itself. +The index lists each symbol defined by a member of a library that is a +relocatable object file. +This speeds up linking to the library, and allows routines in the library +to call each other regardless of their placement within the library. .Sh SEE ALSO +.Xr ar 1 , .Xr cc 1 , .Xr ld 1 , .Xr nm 1 , .Xr intro 2 , .Xr math 3 , -.Xr stdio 3 +.Xr stdio 3 , +.Xr make.conf 5 , +.Xr src.conf 5 .Sh HISTORY An .Nm
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