Hi, I have noticed that the Tiny C Compiler does not not align the stack to 16 bytes on i386 Linux. Unfortunately over the years the ABI defined by gcc has gradually drifted from 4 bytes to 16 bytes. To reproduce see https://sourceforge.net/p/fbc/bugs/659/ (that page is the equivalent issue in freebasic). TCC suffers from the same issue.
I ran into the issue in tcc myself when I attempted to call back from tcc generated code into the Mozilla Spidermonkey JavaScript VM via js-ctypes callbacks. I was able to hack around it in my project with a bit of inline assembly https://github.com/cosinusoidally/mishmashvm/commit/8746e482256af04589bdfcda14d955713f2e3651 but in the general case this is not a complete fix as I may eventually end up calling some affected system library from tcc generated code. I've been luckly so far, but there's a good chance I'll eventually hit this issue again. I did have a stab at implementing something like mstackrealign in tcc, but the code I wrote was subtly buggy (breaks several tests and produces some buggy binaries). Included below in case it is any use as the basis of a real fix: diff --git a/i386-gen.c b/i386-gen.c index 8c245ad..8a33135 100644 --- a/i386-gen.c +++ b/i386-gen.c @@ -402,14 +402,41 @@ ST_FUNC int gfunc_sret(CType *vt, int variadic, CType *ret, int *ret_align, int #endif } +int gfunc_call_realign(){ + // 50 push %eax + o(0x50); + // 89 e0 mov %esp,%eax + o(0x89); o(0xe0); + // 83 c0 04 add $0x4,%eax + o(0x83); o(0xc0); o(0x04); + // 81 e4 f0 ff ff ff and $0xfffffff0,%esp + o(0x81); o(0xe4); o(0xf0); o(0xff); o(0xff); o(0xff); + // 90 nop + int foo1=ind; + o(0x90); + o(0x90); + o(0x90); + // 50 push %eax + o(0x50); + // 8b 40 fc mov -0x4(%eax),%eax + o(0x8b); o(0x40); o(0xfc); + + return foo1; +} + /* Generate function call. The function address is pushed first, then all the parameters in call order. This functions pops all the parameters and the function address. */ ST_FUNC void gfunc_call(int nb_args) { - int size, align, r, args_size, i, func_call; + int size, align, r, args_size, i, func_call,foo1; + int pre=0; Sym *func_sym; - + if(nb_args==0){ + foo1=gfunc_call_realign(); + pre=1; + } + #ifdef CONFIG_TCC_BCHECK if (tcc_state->do_bounds_check) gbound_args(nb_args); @@ -432,6 +459,12 @@ ST_FUNC void gfunc_call(int nb_args) } else #endif { + // insert stack realign + if(pre==0){ + foo1=gfunc_call_realign(); + pre=1; + } + oad(0xec81, size); /* sub $xxx, %esp */ /* generate structure store */ r = get_reg(RC_INT); @@ -443,6 +476,17 @@ ST_FUNC void gfunc_call(int nb_args) args_size += size; } else if (is_float(vtop->type.t)) { gv(RC_FLOAT); /* only one float register */ + + // insert stack realign + if(pre==0){ + foo1=gfunc_call_realign(); + pre=1; + } + if(pre==0){ + foo1=gfunc_call_realign(); + pre=1; + } + if ((vtop->type.t & VT_BTYPE) == VT_FLOAT) size = 4; else if ((vtop->type.t & VT_BTYPE) == VT_DOUBLE) @@ -461,6 +505,13 @@ ST_FUNC void gfunc_call(int nb_args) /* simple type (currently always same size) */ /* XXX: implicit cast ? */ r = gv(RC_INT); + + // insert stack realign + if(pre==0){ + foo1=gfunc_call_realign(); + pre=1; + } + if ((vtop->type.t & VT_BTYPE) == VT_LLONG) { size = 8; o(0x50 + vtop->r2); /* push r */ @@ -505,6 +556,13 @@ ST_FUNC void gfunc_call(int nb_args) if (args_size && func_call != FUNC_STDCALL && func_call != FUNC_FASTCALLW) gadd_sp(args_size); vtop--; + + // 5c pop %esp + o(0x5c); + int blah=(4-(((args_size+4) & 15)>> 2))&3; + for(int bar=0;bar<blah;bar++){ + cur_text_section->data[foo1+bar] = 0x50; + } } #ifdef TCC_TARGET_PE Thanks Liam Wilson
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