diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c index d7c93e3b57..5cea9acd5a 100644 --- a/accel/tcg/translate-all.c +++ b/accel/tcg/translate-all.c @@ -355,6 +355,8 @@ TranslationBlock *tb_gen_code(CPUState *cpu, tcg_ctx->page_bits = TARGET_PAGE_BITS; tcg_ctx->page_mask = TARGET_PAGE_MASK; tcg_ctx->tlb_dyn_max_bits = CPU_TLB_DYN_MAX_BITS; + tcg_ctx->tlb_fast_offset = + (int)offsetof(ArchCPU, neg.tlb.f) - (int)offsetof(ArchCPU, env); #endif tb_overflow: diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h index b757d37966..0d418a0384 100644 --- a/include/exec/cpu-defs.h +++ b/include/exec/cpu-defs.h @@ -61,12 +61,11 @@ #define NB_MMU_MODES 16 #if !defined(CONFIG_USER_ONLY) && defined(CONFIG_TCG) +#include "exec/tlb-common.h" /* use a fully associative victim tlb of 8 entries */ #define CPU_VTLB_SIZE 8 -#define CPU_TLB_ENTRY_BITS 5 - #define CPU_TLB_DYN_MIN_BITS 6 #define CPU_TLB_DYN_DEFAULT_BITS 8 @@ -90,27 +89,6 @@ # endif # endif -/* Minimalized TLB entry for use by TCG fast path. */ -typedef union CPUTLBEntry { - struct { - uint64_t addr_read; - uint64_t addr_write; - uint64_t addr_code; - /* - * Addend to virtual address to get host address. IO accesses - * use the corresponding iotlb value. - */ - uintptr_t addend; - }; - /* - * Padding to get a power of two size, as well as index - * access to addr_{read,write,code}. - */ - uint64_t addr_idx[(1 << CPU_TLB_ENTRY_BITS) / sizeof(uint64_t)]; -} CPUTLBEntry; - -QEMU_BUILD_BUG_ON(sizeof(CPUTLBEntry) != (1 << CPU_TLB_ENTRY_BITS)); - #endif /* !CONFIG_USER_ONLY && CONFIG_TCG */ #if !defined(CONFIG_USER_ONLY) @@ -184,17 +162,6 @@ typedef struct CPUTLBDesc { CPUTLBEntryFull *fulltlb; } CPUTLBDesc; -/* - * Data elements that are per MMU mode, accessed by the fast path. - * The structure is aligned to aid loading the pair with one insn. - */ -typedef struct CPUTLBDescFast { - /* Contains (n_entries - 1) << CPU_TLB_ENTRY_BITS */ - uintptr_t mask; - /* The array of tlb entries itself. */ - CPUTLBEntry *table; -} CPUTLBDescFast QEMU_ALIGNED(2 * sizeof(void *)); - /* * Data elements that are shared between all MMU modes. */ @@ -230,10 +197,6 @@ typedef struct CPUTLB { CPUTLBDescFast f[NB_MMU_MODES]; } CPUTLB; -/* This will be used by TCG backends to compute offsets. */ -#define TLB_MASK_TABLE_OFS(IDX) \ - ((int)offsetof(ArchCPU, neg.tlb.f[IDX]) - (int)offsetof(ArchCPU, env)) - #else typedef struct CPUTLB { } CPUTLB; diff --git a/include/exec/tlb-common.h b/include/exec/tlb-common.h new file mode 100644 index 0000000000..dc5a5faa0b --- /dev/null +++ b/include/exec/tlb-common.h @@ -0,0 +1,56 @@ +/* + * Common definitions for the softmmu tlb + * + * Copyright (c) 2003 Fabrice Bellard + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, see . + */ +#ifndef EXEC_TLB_COMMON_H +#define EXEC_TLB_COMMON_H 1 + +#define CPU_TLB_ENTRY_BITS 5 + +/* Minimalized TLB entry for use by TCG fast path. */ +typedef union CPUTLBEntry { + struct { + uint64_t addr_read; + uint64_t addr_write; + uint64_t addr_code; + /* + * Addend to virtual address to get host address. IO accesses + * use the corresponding iotlb value. + */ + uintptr_t addend; + }; + /* + * Padding to get a power of two size, as well as index + * access to addr_{read,write,code}. + */ + uint64_t addr_idx[(1 << CPU_TLB_ENTRY_BITS) / sizeof(uint64_t)]; +} CPUTLBEntry; + +QEMU_BUILD_BUG_ON(sizeof(CPUTLBEntry) != (1 << CPU_TLB_ENTRY_BITS)); + +/* + * Data elements that are per MMU mode, accessed by the fast path. + * The structure is aligned to aid loading the pair with one insn. + */ +typedef struct CPUTLBDescFast { + /* Contains (n_entries - 1) << CPU_TLB_ENTRY_BITS */ + uintptr_t mask; + /* The array of tlb entries itself. */ + CPUTLBEntry *table; +} CPUTLBDescFast QEMU_ALIGNED(2 * sizeof(void *)); + +#endif /* EXEC_TLB_COMMON_H */ diff --git a/include/tcg/tcg.h b/include/tcg/tcg.h index 0da17f1b4f..54f260a66b 100644 --- a/include/tcg/tcg.h +++ b/include/tcg/tcg.h @@ -547,6 +547,7 @@ struct TCGContext { TCGType addr_type; /* TCG_TYPE_I32 or TCG_TYPE_I64 */ #ifdef CONFIG_SOFTMMU + int tlb_fast_offset; int page_mask; uint8_t page_bits; uint8_t tlb_dyn_max_bits; diff --git a/tcg/aarch64/tcg-target.c.inc b/tcg/aarch64/tcg-target.c.inc index e23c57e2cd..35ca80cd56 100644 --- a/tcg/aarch64/tcg-target.c.inc +++ b/tcg/aarch64/tcg-target.c.inc @@ -1636,6 +1636,9 @@ static bool tcg_out_qemu_st_slow_path(TCGContext *s, TCGLabelQemuLdst *lb) return true; } +/* We expect to use a 7-bit scaled negative offset from ENV. */ +#define MIN_TLB_MASK_TABLE_OFS -512 + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -1674,12 +1677,10 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, ? TCG_TYPE_I64 : TCG_TYPE_I32); /* Load env_tlb(env)->f[mmu_idx].{mask,table} into {tmp0,tmp1}. */ - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -512); QEMU_BUILD_BUG_ON(offsetof(CPUTLBDescFast, mask) != 0); QEMU_BUILD_BUG_ON(offsetof(CPUTLBDescFast, table) != 8); tcg_out_insn(s, 3314, LDP, TCG_REG_TMP0, TCG_REG_TMP1, TCG_AREG0, - TLB_MASK_TABLE_OFS(mem_index), 1, 0); + tlb_mask_table_ofs(s, mem_index), 1, 0); /* Extract the TLB index from the address into X0. */ tcg_out_insn(s, 3502S, AND_LSR, mask_type == TCG_TYPE_I64, diff --git a/tcg/arm/tcg-target.c.inc b/tcg/arm/tcg-target.c.inc index 64eb0cb5dc..83e286088f 100644 --- a/tcg/arm/tcg-target.c.inc +++ b/tcg/arm/tcg-target.c.inc @@ -1374,6 +1374,9 @@ static bool tcg_out_qemu_st_slow_path(TCGContext *s, TCGLabelQemuLdst *lb) return true; } +/* We expect to use an 9-bit sign-magnitude negative offset from ENV. */ +#define MIN_TLB_MASK_TABLE_OFS -256 + static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, TCGReg addrlo, TCGReg addrhi, MemOpIdx oi, bool is_ld) @@ -1405,7 +1408,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, int mem_index = get_mmuidx(oi); int cmp_off = is_ld ? offsetof(CPUTLBEntry, addr_read) : offsetof(CPUTLBEntry, addr_write); - int fast_off = TLB_MASK_TABLE_OFS(mem_index); + int fast_off = tlb_mask_table_ofs(s, mem_index); unsigned s_mask = (1 << (opc & MO_SIZE)) - 1; TCGReg t_addr; @@ -1416,8 +1419,6 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, ldst->addrhi_reg = addrhi; /* Load env_tlb(env)->f[mmu_idx].{mask,table} into {r0,r1}. */ - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -256); QEMU_BUILD_BUG_ON(offsetof(CPUTLBDescFast, mask) != 0); QEMU_BUILD_BUG_ON(offsetof(CPUTLBDescFast, table) != 4); tcg_out_ldrd_8(s, COND_AL, TCG_REG_R0, TCG_AREG0, fast_off); diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc index ae54e5fbf3..ab997b5fb3 100644 --- a/tcg/i386/tcg-target.c.inc +++ b/tcg/i386/tcg-target.c.inc @@ -1900,6 +1900,8 @@ static inline int setup_guest_base_seg(void) #endif /* setup_guest_base_seg */ #endif /* !SOFTMMU */ +#define MIN_TLB_MASK_TABLE_OFS INT_MIN + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -1934,6 +1936,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, int trexw = 0, hrexw = 0, tlbrexw = 0; unsigned mem_index = get_mmuidx(oi); unsigned s_mask = (1 << s_bits) - 1; + int fast_ofs = tlb_mask_table_ofs(s, mem_index); int tlb_mask; ldst = new_ldst_label(s); @@ -1959,12 +1962,10 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, s->page_bits - CPU_TLB_ENTRY_BITS); tcg_out_modrm_offset(s, OPC_AND_GvEv + trexw, TCG_REG_L0, TCG_AREG0, - TLB_MASK_TABLE_OFS(mem_index) + - offsetof(CPUTLBDescFast, mask)); + fast_ofs + offsetof(CPUTLBDescFast, mask)); tcg_out_modrm_offset(s, OPC_ADD_GvEv + hrexw, TCG_REG_L0, TCG_AREG0, - TLB_MASK_TABLE_OFS(mem_index) + - offsetof(CPUTLBDescFast, table)); + fast_ofs + offsetof(CPUTLBDescFast, table)); /* * If the required alignment is at least as large as the access, simply diff --git a/tcg/loongarch64/tcg-target.c.inc b/tcg/loongarch64/tcg-target.c.inc index e89f3b848b..baf5fc3819 100644 --- a/tcg/loongarch64/tcg-target.c.inc +++ b/tcg/loongarch64/tcg-target.c.inc @@ -834,6 +834,9 @@ bool tcg_target_has_memory_bswap(MemOp memop) return false; } +/* We expect to use a 12-bit negative offset from ENV. */ +#define MIN_TLB_MASK_TABLE_OFS -(1 << 11) + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -855,7 +858,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, #ifdef CONFIG_SOFTMMU unsigned s_bits = opc & MO_SIZE; int mem_index = get_mmuidx(oi); - int fast_ofs = TLB_MASK_TABLE_OFS(mem_index); + int fast_ofs = tlb_mask_table_ofs(s, mem_index); int mask_ofs = fast_ofs + offsetof(CPUTLBDescFast, mask); int table_ofs = fast_ofs + offsetof(CPUTLBDescFast, table); @@ -864,8 +867,6 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, ldst->oi = oi; ldst->addrlo_reg = addr_reg; - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -(1 << 11)); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP0, TCG_AREG0, mask_ofs); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP1, TCG_AREG0, table_ofs); diff --git a/tcg/mips/tcg-target.c.inc b/tcg/mips/tcg-target.c.inc index 4c0de0a380..9faa8bdf0b 100644 --- a/tcg/mips/tcg-target.c.inc +++ b/tcg/mips/tcg-target.c.inc @@ -1254,6 +1254,9 @@ bool tcg_target_has_memory_bswap(MemOp memop) return false; } +/* We expect to use a 16-bit negative offset from ENV. */ +#define MIN_TLB_MASK_TABLE_OFS -32768 + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -1279,7 +1282,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, #ifdef CONFIG_SOFTMMU unsigned s_mask = (1 << s_bits) - 1; int mem_index = get_mmuidx(oi); - int fast_off = TLB_MASK_TABLE_OFS(mem_index); + int fast_off = tlb_mask_table_ofs(s, mem_index); int mask_off = fast_off + offsetof(CPUTLBDescFast, mask); int table_off = fast_off + offsetof(CPUTLBDescFast, table); int add_off = offsetof(CPUTLBEntry, addend); @@ -1293,8 +1296,6 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, ldst->addrhi_reg = addrhi; /* Load tlb_mask[mmu_idx] and tlb_table[mmu_idx]. */ - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -32768); tcg_out_ld(s, TCG_TYPE_PTR, TCG_TMP0, TCG_AREG0, mask_off); tcg_out_ld(s, TCG_TYPE_PTR, TCG_TMP1, TCG_AREG0, table_off); diff --git a/tcg/ppc/tcg-target.c.inc b/tcg/ppc/tcg-target.c.inc index 73f6ea0393..507fe6cda8 100644 --- a/tcg/ppc/tcg-target.c.inc +++ b/tcg/ppc/tcg-target.c.inc @@ -2036,6 +2036,9 @@ bool tcg_target_has_memory_bswap(MemOp memop) return aa.atom <= MO_64; } +/* We expect to use a 16-bit negative offset from ENV. */ +#define MIN_TLB_MASK_TABLE_OFS -32768 + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -2072,7 +2075,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, int mem_index = get_mmuidx(oi); int cmp_off = is_ld ? offsetof(CPUTLBEntry, addr_read) : offsetof(CPUTLBEntry, addr_write); - int fast_off = TLB_MASK_TABLE_OFS(mem_index); + int fast_off = tlb_mask_table_ofs(s, mem_index); int mask_off = fast_off + offsetof(CPUTLBDescFast, mask); int table_off = fast_off + offsetof(CPUTLBDescFast, table); @@ -2083,8 +2086,6 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, ldst->addrhi_reg = addrhi; /* Load tlb_mask[mmu_idx] and tlb_table[mmu_idx]. */ - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -32768); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP1, TCG_AREG0, mask_off); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP2, TCG_AREG0, table_off); diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc index a6d56e2d0e..eeaeb6b6e3 100644 --- a/tcg/riscv/tcg-target.c.inc +++ b/tcg/riscv/tcg-target.c.inc @@ -1185,6 +1185,9 @@ static bool tcg_out_qemu_st_slow_path(TCGContext *s, TCGLabelQemuLdst *l) return true; } +/* We expect to use a 12-bit negative offset from ENV. */ +#define MIN_TLB_MASK_TABLE_OFS -(1 << 11) + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -1208,7 +1211,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, TCGReg *pbase, unsigned s_bits = opc & MO_SIZE; unsigned s_mask = (1u << s_bits) - 1; int mem_index = get_mmuidx(oi); - int fast_ofs = TLB_MASK_TABLE_OFS(mem_index); + int fast_ofs = tlb_mask_table_ofs(s, mem_index); int mask_ofs = fast_ofs + offsetof(CPUTLBDescFast, mask); int table_ofs = fast_ofs + offsetof(CPUTLBDescFast, table); int compare_mask; @@ -1219,8 +1222,6 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, TCGReg *pbase, ldst->oi = oi; ldst->addrlo_reg = addr_reg; - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -(1 << 11)); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP0, TCG_AREG0, mask_ofs); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP1, TCG_AREG0, table_ofs); diff --git a/tcg/s390x/tcg-target.c.inc b/tcg/s390x/tcg-target.c.inc index 03be800c3b..aeddebbb5c 100644 --- a/tcg/s390x/tcg-target.c.inc +++ b/tcg/s390x/tcg-target.c.inc @@ -1735,6 +1735,9 @@ static bool tcg_out_qemu_st_slow_path(TCGContext *s, TCGLabelQemuLdst *lb) return true; } +/* We're expecting to use a 20-bit negative offset on the tlb memory ops. */ +#define MIN_TLB_MASK_TABLE_OFS -(1 << 19) + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -1757,7 +1760,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, #ifdef CONFIG_SOFTMMU unsigned s_mask = (1 << s_bits) - 1; int mem_index = get_mmuidx(oi); - int fast_off = TLB_MASK_TABLE_OFS(mem_index); + int fast_off = tlb_mask_table_ofs(s, mem_index); int mask_off = fast_off + offsetof(CPUTLBDescFast, mask); int table_off = fast_off + offsetof(CPUTLBDescFast, table); int ofs, a_off; @@ -1771,8 +1774,6 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, tcg_out_sh64(s, RSY_SRLG, TCG_TMP0, addr_reg, TCG_REG_NONE, s->page_bits - CPU_TLB_ENTRY_BITS); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -(1 << 19)); tcg_out_insn(s, RXY, NG, TCG_TMP0, TCG_AREG0, TCG_REG_NONE, mask_off); tcg_out_insn(s, RXY, AG, TCG_TMP0, TCG_AREG0, TCG_REG_NONE, table_off); diff --git a/tcg/sparc64/tcg-target.c.inc b/tcg/sparc64/tcg-target.c.inc index 6c60657c36..ffcb879211 100644 --- a/tcg/sparc64/tcg-target.c.inc +++ b/tcg/sparc64/tcg-target.c.inc @@ -1017,6 +1017,9 @@ bool tcg_target_has_memory_bswap(MemOp memop) return true; } +/* We expect to use a 13-bit negative offset from ENV. */ +#define MIN_TLB_MASK_TABLE_OFS -(1 << 12) + /* * For softmmu, perform the TLB load and compare. * For useronly, perform any required alignment tests. @@ -1040,7 +1043,7 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, #ifdef CONFIG_SOFTMMU int mem_index = get_mmuidx(oi); - int fast_off = TLB_MASK_TABLE_OFS(mem_index); + int fast_off = tlb_mask_table_ofs(s, mem_index); int mask_off = fast_off + offsetof(CPUTLBDescFast, mask); int table_off = fast_off + offsetof(CPUTLBDescFast, table); int cmp_off = is_ld ? offsetof(CPUTLBEntry, addr_read) @@ -1050,8 +1053,6 @@ static TCGLabelQemuLdst *prepare_host_addr(TCGContext *s, HostAddress *h, int cc; /* Load tlb_mask[mmu_idx] and tlb_table[mmu_idx]. */ - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) > 0); - QEMU_BUILD_BUG_ON(TLB_MASK_TABLE_OFS(0) < -(1 << 12)); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_T2, TCG_AREG0, mask_off); tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_T3, TCG_AREG0, table_off); diff --git a/tcg/tcg.c b/tcg/tcg.c index 2352ca4ade..2d17c09aea 100644 --- a/tcg/tcg.c +++ b/tcg/tcg.c @@ -41,6 +41,7 @@ #define NO_CPU_IO_DEFS #include "exec/exec-all.h" +#include "exec/tlb-common.h" #include "tcg/tcg-op.h" #if UINTPTR_MAX == UINT32_MAX @@ -407,6 +408,13 @@ static uintptr_t G_GNUC_UNUSED get_jmp_target_addr(TCGContext *s, int which) return (uintptr_t)tcg_splitwx_to_rx(&s->gen_tb->jmp_target_addr[which]); } +#if defined(CONFIG_SOFTMMU) && !defined(CONFIG_TCG_INTERPRETER) +static int tlb_mask_table_ofs(TCGContext *s, int which) +{ + return s->tlb_fast_offset + which * sizeof(CPUTLBDescFast); +} +#endif + /* Signal overflow, starting over with fewer guest insns. */ static G_NORETURN void tcg_raise_tb_overflow(TCGContext *s) @@ -1521,6 +1529,11 @@ void tcg_func_start(TCGContext *s) tcg_debug_assert(s->addr_type == TCG_TYPE_I32 || s->addr_type == TCG_TYPE_I64); + +#if defined(CONFIG_SOFTMMU) && !defined(CONFIG_TCG_INTERPRETER) + tcg_debug_assert(s->tlb_fast_offset < 0); + tcg_debug_assert(s->tlb_fast_offset >= MIN_TLB_MASK_TABLE_OFS); +#endif } static TCGTemp *tcg_temp_alloc(TCGContext *s)