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Moved build instructions from the man page

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Some requirements and build hints for assembler modules compilation were
moved from doc/man3/OPENSSL_ia32cap.pod to INSTALL.md.

Fixes #14674

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14683)
This commit is contained in:
Andrey Matyukov 2021-03-25 14:46:13 +03:00 committed by Tomas Mraz
parent 92a979b403
commit 203c18f14a
2 changed files with 38 additions and 32 deletions
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40
INSTALL.md
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@ -41,6 +41,7 @@ Table of Contents
- [Notes on multi-threading](#notes-on-multi-threading)
- [Notes on shared libraries](#notes-on-shared-libraries)
- [Notes on random number generation](#notes-on-random-number-generation)
- [Notes on assembler modules compilation](#notes-on-assembler-modules-compilation)
Prerequisites
=============
@ -1610,8 +1611,8 @@ build. Use this command:
$ mms clean ! (or mmk) OpenVMS
$ nmake clean # Windows
Assembler error messages can sometimes be sidestepped by using the
`no-asm` configuration option.
Assembler error messages can sometimes be sidestepped by using the `no-asm`
configuration option. See also [notes](#notes-on-assembler-modules-compilation).
Compiling parts of OpenSSL with gcc and others with the system compiler will
result in unresolved symbols on some systems.
@ -1734,6 +1735,41 @@ to install additional support software to obtain a random seed and reseed
the CSPRNG manually. Please check out the manual pages for `RAND_add()`,
`RAND_bytes()`, `RAND_egd()`, and the FAQ for more information.
Notes on assembler modules compilation
--------------------------------------
Compilation of some code paths in assembler modules might depend on whether the
current assembler version supports certain ISA extensions or not. Code paths
that use the AES-NI, PCLMULQDQ, SSSE3, and SHA extensions are always assembled.
Apart from that, the minimum requirements for the assembler versions are shown
in the table below:
| ISA extension | GNU as | nasm | llvm |
|---------------|--------|--------|---------|
| AVX | 2.19 | 2.09 | 3.0 |
| AVX2 | 2.22 | 2.10 | 3.1 |
| ADCX/ADOX | 2.23 | 2.10 | 3.3 |
| AVX512 | 2.25 | 2.11.8 | 3.6 (*) |
| AVX512IFMA | 2.26 | 2.11.8 | 6.0 (*) |
| VAES | 2.30 | 2.13.3 | 6.0 (*) |
---
(*) Even though AVX512 support was implemented in llvm 3.6, prior to version 7.0
an explicit -march flag was apparently required to compile assembly modules. But
then the compiler generates processor-specific code, which in turn contradicts
the idea of performing dispatch at run-time, which is facilitated by the special
variable `OPENSSL_ia32cap`. For versions older than 7.0, it is possible to work
around the problem by forcing the build procedure to use the following script:
#!/bin/sh
exec clang -no-integrated-as "$@"
instead of the real clang. In which case it doesn't matter what clang version
is used, as it is the version of the GNU assembler that will be checked.
---
<!-- Links -->
[openssl-users]:

30
doc/man3/OPENSSL_ia32cap.pod
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@ -121,36 +121,6 @@ setting up B<OPENSSL_ia32cap> environment variable. For example assigning
C<:~0x20> would disable AVX2 code paths, and C<:0> - all post-AVX
extensions.
It should be noted that whether or not some of the most "fancy"
extension code paths are actually assembled depends on current assembler
version. Base minimum of AES-NI/PCLMULQDQ, SSSE3 and SHA extension code
paths are always assembled. Apart from that, minimum assembler version
requirements are summarized in below table:
Extension | GNU as | nasm | llvm
------------+--------+--------+--------
AVX | 2.19 | 2.09 | 3.0
AVX2 | 2.22 | 2.10 | 3.1
ADCX/ADOX | 2.23 | 2.10 | 3.3
AVX512 | 2.25 | 2.11.8 | see NOTES
AVX512IFMA | 2.26 | 2.11.8 | see NOTES
VAES | 2.30 | 2.13.3 |
=head1 NOTES
Even though AVX512 support was implemented in llvm 3.6, compilation of
assembly modules apparently requires explicit -march flag. But then
compiler generates processor-specific code, which in turn contradicts
the mere idea of run-time switch execution facilitated by the variable
in question. Till the limitation is lifted, it's possible to work around
the problem by making build procedure use following script:
#!/bin/sh
exec clang -no-integrated-as "$@"
instead of real clang. In which case it doesn't matter which clang
version is used, as it is GNU assembler version that will be checked.
=head1 RETURN VALUES
Not available.