Replace unavailable flag-preserving instruction #193

Merged

foopub merged 2 commits from patch-1 into develop

2021-02-27 12:07:57 -06:00

foopub commented

2021-02-25 19:43:51 -06:00

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It seems sub requires thumb2 instructions which are unavailable. This is in line with the rest of the sdk code base which uses subs.

kilograham commented

2021-02-26 07:32:19 -06:00

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some context needed here. why is this failing for you? I'm guessing you are perhaps trying to build with clang?

foopub commented

2021-02-26 09:52:29 -06:00

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Yes, I'm trying to compile with clang.
I don't know if this is of any use, but the disassembly of the gcc binary with sub has this:

157   62:   3001            adds    r0, #1
158   64:   3801            subs    r0, #1
159   66:   d1fd            bne.n   64 <clock_configure+0x64>

while the clang with subs it's:

 95   86:   1c40            adds    r0, r0, #1
 96   88:   3801            subs    r0, #1
 97   8a:   d1fd            bne.n   88 <clock_configure+0x88>

so it shouldn't make a difference to bne?

Also, I realised I was testing with the -masm-syntax-unified option on gcc, so I'll change the commit to include
".syntax unified\n\t"
which I've tested and it works with the normal cmake.

Yes, I'm trying to compile with clang. I don't know if this is of any use, but the disassembly of the gcc binary with `sub` has this: ``` 157 62: 3001 adds r0, #1 158 64: 3801 subs r0, #1 159 66: d1fd bne.n 64 <clock_configure+0x64> ``` while the clang with `subs` it's: ``` 95 86: 1c40 adds r0, r0, #1 96 88: 3801 subs r0, #1 97 8a: d1fd bne.n 88 <clock_configure+0x88> ``` so it shouldn't make a difference to `bne`? Also, I realised I was testing with the -masm-syntax-unified option on gcc, so I'll change the commit to include `".syntax unified\n\t"` which I've tested and it works with the normal cmake.

kilograham commented

2021-02-26 11:54:50 -06:00

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Yes the fact that it was converted to a subs was a good thing, since sub would never have worked.

I was going to suggest .syntax unified but wanted to make sure what you were doing first.

Yes the fact that it was converted to a `subs` was a good thing, since `sub` would never have worked. I was going to suggest `.syntax unified` but wanted to make sure what you were doing first.

kilograham commented

2021-02-26 11:55:45 -06:00

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