Re: How to re-compile sshd for a 386

On Fri, 1 Aug 2025, Greg Troxel wrote:

> Beware that openssl has a habit of trying instructions, catching faults,
> and using them if they work.  At least I noticed this on earmv7.  That
> may have something to do with this.
>

Not on x86. It does that on ARM, PPC, S390x and SPARCv8. On x86 it relies on
the CPUID instruction, which would be a problem on any x86 below Pentium.

On Fri, 1 Aug 2025, Mark Ter Morshuizen wrote:

> The only problem I have is that when the system starts up sshd fails with 
> "illegal instruction" and does not start.
>

Prolly when executing the CPUID or MMX/SSE code in libcrypto.so. What branch is
this source from?

> Is there a way to recompile the built in (not a package) sshd so that it runs 
> on the 386?
>

You'll have to pass the `-march=i386' flag to GCC and use the portable C
routines in libcrypto instead of the preferred faster assembly code.

For example in -HEAD, see:

```
$ egrep -r '(CPUID|_ASM)' /usr/src/crypto/external/bsd/openssl/lib/libcrypto/
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/crypto.inc:.if !defined(CPUID)
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/crypto.inc:CRYPTO_SRCS+=  ${CPUID_SRCS}
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/engine.inc:.if !defined(CPUID)
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/engine.inc:CRYPTOCPPFLAGS+=-DNEED_CPUID_SETUP
[...]
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/arm/sha.inc:SHACPPFLAGS = -DSHA1_ASM -DSHA256_ASM -DSHA512_ASM -DKECCAK1600_ASM
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/aes.inc:AESCPPFLAGS = -DAES_ASM -DOPENSSL_IA32_SSE2
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/bn.inc:BNCPPFLAGS+= -DOPENSSL_BN_ASM_PART_WORDS
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/crypto.inc:CPUID_SRCS = x86cpuid.S
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/crypto.inc:CPUID = yes
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/crypto.inc:CPPFLAGS += -DOPENSSL_CPUID_OBJ
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/ec.inc:ECCPPFLAGS+= -DECP_NISTZ256_ASM
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/modes.inc:MODESCPPFLAGS = -DGHASH_ASM -DOPENSSL_IA32_SSE2
/usr/src/crypto/external/bsd/openssl/lib/libcrypto/arch/i386/poly1305.inc:POLY1305_CPPFLAGS+=-DPOLY1305_ASM
[...]
$
```


> (I have the same 4.0.1 release on a virtual machine. How do I 
> make it compile sshd for the 386 and not for itself? Preferably without 
> having to build the entire system.)
>

It's a pain, but, it can be done. You'll have to compile everything OpenSSH
depends on first, then sshd itself with `-march=i386'. I did this awhile back
but never wrote down the exact commands--but it's easy enough to recreate...

-RVP