Re: [Tarantool-patches] [PATCH luajit 09/19] FFI: Eliminate hardcoded string hashes.

[Maxim Kokryashkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Hi, Sergey!
Thanks for the patch!
LGTM, except for a few comments below.

On Wed, Aug 09, 2023 at 06:35:58PM +0300, Sergey Kaplun via Tarantool-patches wrote:
> From: Mike Pall <mike>
> 
> (cherry-picked from commit 70f4b15ee45a6137fe6b48b941faea79d72f7159)
> 
> This patch refactors FFI parsing of supported C attributes and pragmas,
> `ffi.abi()` parameter check. It replaces usage of comparison (with
Typo: s/usage/the usage/
> hardcoded string hashes) with search in the given string with the
Typo: s/with search/with a search/
> format: "\XXXattribute1\XXXattribute2", where `\XXX` is the length of
> "attribute" name.
> 
> Sergey Kaplun:
> * added the description for the commit
> 
> Part of tarantool/tarantool#8825
> ---
>  src/lib_ffi.c   | 35 ++++++++++------------
>  src/lj_cparse.c | 77 +++++++++++++++++++++++++++++++------------------
>  src/lj_cparse.h |  2 ++
>  3 files changed, 67 insertions(+), 47 deletions(-)
> 
> diff --git a/src/lib_ffi.c b/src/lib_ffi.c
> index d1fe1a14..62af54c1 100644
> --- a/src/lib_ffi.c
> +++ b/src/lib_ffi.c
> @@ -720,50 +720,47 @@ LJLIB_CF(ffi_fill)	LJLIB_REC(.)
>    return 0;
>  }
>  
> -#define H_(le, be)	LJ_ENDIAN_SELECT(0x##le, 0x##be)
> -
>  /* Test ABI string. */
>  LJLIB_CF(ffi_abi)	LJLIB_REC(.)
>  {
>    GCstr *s = lj_lib_checkstr(L, 1);
> -  int b = 0;
> -  switch (s->hash) {
> +  int b = lj_cparse_case(s,
>  #if LJ_64
> -  case H_(849858eb,ad35fd06): b = 1; break;  /* 64bit */
> +    "\00564bit"
>  #else
> -  case H_(662d3c79,d0e22477): b = 1; break;  /* 32bit */
> +    "\00532bit"
>  #endif
>  #if LJ_ARCH_HASFPU
> -  case H_(e33ee463,e33ee463): b = 1; break;  /* fpu */
> +    "\003fpu"
>  #endif
>  #if LJ_ABI_SOFTFP
> -  case H_(61211a23,c2e8c81c): b = 1; break;  /* softfp */
> +    "\006softfp"
>  #else
> -  case H_(539417a8,8ce0812f): b = 1; break;  /* hardfp */
> +    "\006hardfp"
>  #endif
>  #if LJ_ABI_EABI
> -  case H_(2182df8f,f2ed1152): b = 1; break;  /* eabi */
> +    "\004eabi"
>  #endif
>  #if LJ_ABI_WIN
> -  case H_(4ab624a8,4ab624a8): b = 1; break;  /* win */
> +    "\003win"
>  #endif
>  #if LJ_TARGET_UWP
> -  case H_(a40f0bcb,a40f0bcb): b = 1; break;  /* uwp */
> +    "\003uwp"
> +#endif
> +#if LJ_LE
> +    "\002le"
> +#else
> +    "\002be"
>  #endif
> -  case H_(3af93066,1f001464): b = 1; break;  /* le/be */
>  #if LJ_GC64
> -  case H_(9e89d2c9,13c83c92): b = 1; break;  /* gc64 */
> +    "\004gc64"
>  #endif
> -  default:
> -    break;
> -  }
> +  ) >= 0;
>    setboolV(L->top-1, b);
>    setboolV(&G(L)->tmptv2, b);  /* Remember for trace recorder. */
>    return 1;
>  }
>  
> -#undef H_
> -
>  LJLIB_PUSH(top-8) LJLIB_SET(!)  /* Store reference to miscmap table. */
>  
>  LJLIB_CF(ffi_metatype)
> diff --git a/src/lj_cparse.c b/src/lj_cparse.c
> index fb440567..07c643d4 100644
> --- a/src/lj_cparse.c
> +++ b/src/lj_cparse.c
> @@ -28,6 +28,24 @@
>  ** If in doubt, please check the input against your favorite C compiler.
>  */
>  
> +/* -- Miscellaneous ------------------------------------------------------- */
> +
> +/* Match string against a C literal. */
> +#define cp_str_is(str, k) \
> +  ((str)->len == sizeof(k)-1 && !memcmp(strdata(str), k, sizeof(k)-1))
> +
> +/* Check string against a linear list of matches. */
> +int lj_cparse_case(GCstr *str, const char *match)
> +{
> +  MSize len;
> +  int n;
> +  for  (n = 0; (len = (MSize)*match++); n++, match += len) {
> +    if (str->len == len && !memcmp(match, strdata(str), len))
> +      return n;
> +  }
> +  return -1;
> +}
> +
>  /* -- C lexer ------------------------------------------------------------- */
>  
>  /* C lexer token names. */
> @@ -930,8 +948,6 @@ static CTypeID cp_decl_intern(CPState *cp, CPDecl *decl)
>  
>  /* -- C declaration parser ------------------------------------------------ */
>  
> -#define H_(le, be)	LJ_ENDIAN_SELECT(0x##le, 0x##be)
> -
>  /* Reset declaration state to declaration specifier. */
>  static void cp_decl_reset(CPDecl *decl)
>  {
> @@ -1071,44 +1087,57 @@ static void cp_decl_gccattribute(CPState *cp, CPDecl *decl)
>  	attrstr = lj_str_new(cp->L, c+2, attrstr->len-4);
>  #endif
>        cp_next(cp);
> -      switch (attrstr->hash) {
> -      case H_(64a9208e,8ce14319): case H_(8e6331b2,95a282af):  /* aligned */
> +      switch (lj_cparse_case(attrstr,
> +		"\007aligned" "\013__aligned__"
> +		"\006packed" "\012__packed__"
> +		"\004mode" "\010__mode__"
> +		"\013vector_size" "\017__vector_size__"
> +#if LJ_TARGET_X86
> +		"\007regparm" "\013__regparm__"
> +		"\005cdecl"  "\011__cdecl__"
> +		"\010thiscall" "\014__thiscall__"
> +		"\010fastcall" "\014__fastcall__"
> +		"\007stdcall" "\013__stdcall__"
> +		"\012sseregparm" "\016__sseregparm__"
> +#endif
> +	      )) {
> +      case 0: case 1: /* aligned */
>  	cp_decl_align(cp, decl);
>  	break;
> -      case H_(42eb47de,f0ede26c): case H_(29f48a09,cf383e0c):  /* packed */
> +      case 2: case 3: /* packed */
>  	decl->attr |= CTFP_PACKED;
>  	break;
> -      case H_(0a84eef6,8dfab04c): case H_(995cf92c,d5696591):  /* mode */
> +      case 4: case 5: /* mode */
>  	cp_decl_mode(cp, decl);
>  	break;
> -      case H_(0ab31997,2d5213fa): case H_(bf875611,200e9990):  /* vector_size */
> +      case 6: case 7: /* vector_size */
>  	{
>  	  CTSize vsize = cp_decl_sizeattr(cp);
>  	  if (vsize) CTF_INSERT(decl->attr, VSIZEP, lj_fls(vsize));
>  	}
>  	break;
>  #if LJ_TARGET_X86
> -      case H_(5ad22db8,c689b848): case H_(439150fa,65ea78cb):  /* regparm */
> +      case 8: case 9: /* regparm */
>  	CTF_INSERT(decl->fattr, REGPARM, cp_decl_sizeattr(cp));
>  	decl->fattr |= CTFP_CCONV;
>  	break;
> -      case H_(18fc0b98,7ff4c074): case H_(4e62abed,0a747424):  /* cdecl */
> +      case 10: case 11: /* cdecl */
>  	CTF_INSERT(decl->fattr, CCONV, CTCC_CDECL);
>  	decl->fattr |= CTFP_CCONV;
>  	break;
> -      case H_(72b2e41b,494c5a44): case H_(f2356d59,f25fc9bd):  /* thiscall */
> +      case 12: case 13: /* thiscall */
>  	CTF_INSERT(decl->fattr, CCONV, CTCC_THISCALL);
>  	decl->fattr |= CTFP_CCONV;
>  	break;
> -      case H_(0d0ffc42,ab746f88): case H_(21c54ba1,7f0ca7e3):  /* fastcall */
> +      case 14: case 15: /* fastcall */
>  	CTF_INSERT(decl->fattr, CCONV, CTCC_FASTCALL);
>  	decl->fattr |= CTFP_CCONV;
>  	break;
> -      case H_(ef76b040,9412e06a): case H_(de56697b,c750e6e1):  /* stdcall */
> +      case 16: case 17: /* stdcall */
>  	CTF_INSERT(decl->fattr, CCONV, CTCC_STDCALL);
>  	decl->fattr |= CTFP_CCONV;
>  	break;
> -      case H_(ea78b622,f234bd8e): case H_(252ffb06,8d50f34b):  /* sseregparm */
> +      case 18: case 19: /* sseregparm */
>  	decl->fattr |= CTF_SSEREGPARM;
>  	decl->fattr |= CTFP_CCONV;
>  	break;
> @@ -1140,16 +1169,13 @@ static void cp_decl_msvcattribute(CPState *cp, CPDecl *decl)
>    while (cp->tok == CTOK_IDENT) {
>      GCstr *attrstr = cp->str;
>      cp_next(cp);
> -    switch (attrstr->hash) {
> -    case H_(bc2395fa,98f267f8):  /* align */
> +    if (cp_str_is(attrstr, "align")) {
>        cp_decl_align(cp, decl);
> -      break;
> -    default:  /* Ignore all other attributes. */
> +    } else {  /* Ignore all other attributes. */
>        if (cp_opt(cp, '(')) {
>  	while (cp->tok != ')' && cp->tok != CTOK_EOF) cp_next(cp);
>  	cp_check(cp, ')');
>        }
> -      break;
>      }
>    }
>    cp_check(cp, ')');
> @@ -1729,17 +1755,16 @@ static CTypeID cp_decl_abstract(CPState *cp)
>  static void cp_pragma(CPState *cp, BCLine pragmaline)
>  {
>    cp_next(cp);
> -  if (cp->tok == CTOK_IDENT &&
> -      cp->str->hash == H_(e79b999f,42ca3e85))  {  /* pack */
> +  if (cp->tok == CTOK_IDENT && cp_str_is(cp->str, "pack"))  {
>      cp_next(cp);
>      cp_check(cp, '(');
>      if (cp->tok == CTOK_IDENT) {
> -      if (cp->str->hash == H_(738e923c,a1b65954)) {  /* push */
> +      if (cp_str_is(cp->str, "push")) {
>  	if (cp->curpack < CPARSE_MAX_PACKSTACK) {
>  	  cp->packstack[cp->curpack+1] = cp->packstack[cp->curpack];
>  	  cp->curpack++;
>  	}
> -      } else if (cp->str->hash == H_(6c71cf27,6c71cf27)) {  /* pop */
> +      } else if (cp_str_is(cp->str, "pop")) {
>  	if (cp->curpack > 0) cp->curpack--;
>        } else {
>  	cp_errmsg(cp, cp->tok, LJ_ERR_XSYMBOL);
> @@ -1788,13 +1813,11 @@ static void cp_decl_multi(CPState *cp)
>        if (tok == CTOK_INTEGER) {
>  	cp_line(cp, hashline);
>  	continue;
> -      } else if (tok == CTOK_IDENT &&
> -		 cp->str->hash == H_(187aab88,fcb60b42)) { /* line */
> +      } else if (tok == CTOK_IDENT && cp_str_is(cp->str, "line")) {
>  	if (cp_next(cp) != CTOK_INTEGER) cp_err_token(cp, tok);
>  	cp_line(cp, hashline);
>  	continue;
> -      } else if (tok == CTOK_IDENT &&
> -	  cp->str->hash == H_(f5e6b4f8,1d509107)) { /* pragma */
> +      } else if (tok == CTOK_IDENT && cp_str_is(cp->str, "pragma")) {
>  	cp_pragma(cp, hashline);
>  	continue;
>        } else {
> @@ -1865,8 +1888,6 @@ static void cp_decl_single(CPState *cp)
>    if (cp->tok != CTOK_EOF) cp_err_token(cp, CTOK_EOF);
>  }
>  
> -#undef H_
> -
>  /* ------------------------------------------------------------------------ */
>  
>  /* Protected callback for C parser. */
> diff --git a/src/lj_cparse.h b/src/lj_cparse.h
> index bad1060b..e40b4047 100644
> --- a/src/lj_cparse.h
> +++ b/src/lj_cparse.h
> @@ -60,6 +60,8 @@ typedef struct CPState {
>  
>  LJ_FUNC int lj_cparse(CPState *cp);
>  
> +LJ_FUNC int lj_cparse_case(GCstr *str, const char *match);
> +
>  #endif
>  
>  #endif
> -- 
> 2.41.0
>