From: Ben Pfaff Date: Thu, 2 Sep 2004 22:41:32 +0000 (+0000) Subject: Fix leak. Add comments. Restructure slightly. X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fff78daad97b593a531b54103e3fc335bd3239db;p=pintos-anon Fix leak. Add comments. Restructure slightly. --- diff --git a/src/userprog/addrspace.c b/src/userprog/addrspace.c index 3fa6777..2574c31 100644 --- a/src/userprog/addrspace.c +++ b/src/userprog/addrspace.c @@ -12,18 +12,19 @@ #include "tss.h" /* We load ELF binaries. The following definitions are taken - from the ELF specification, [ELF], more-or-less verbatim. */ + from the ELF specification, [ELF1], more-or-less verbatim. */ -/* ELF types. */ +/* ELF types. See [ELF1] 1-2. */ typedef uint32_t Elf32_Word, Elf32_Addr, Elf32_Off; typedef uint16_t Elf32_Half; -#define PE32Wx PRIx32 -#define PE32Ax PRIx32 -#define PE32Ox PRIx32 -#define PE32Hx PRIx16 +/* For use with ELF types in printk(). */ +#define PE32Wx PRIx32 /* Print Elf32_Word in hexadecimal. */ +#define PE32Ax PRIx32 /* Print Elf32_Addr in hexadecimal. */ +#define PE32Ox PRIx32 /* Print Elf32_Off in hexadecimal. */ +#define PE32Hx PRIx16 /* Print Elf32_Half in hexadecimal. */ -/* Executable header. +/* Executable header. See [ELF1] 1-4 to 1-8. This appears at the very beginning of an ELF binary. */ struct Elf32_Ehdr { @@ -43,8 +44,9 @@ struct Elf32_Ehdr Elf32_Half e_shstrndx; }; -/* Program header. - There are e_phnum of these, starting at file offset e_phoff. */ +/* Program header. See [ELF1] 2-2 to 2-4. + There are e_phnum of these, starting at file offset e_phoff + (see [ELF1] 1-6). */ struct Elf32_Phdr { Elf32_Word p_type; @@ -57,7 +59,7 @@ struct Elf32_Phdr Elf32_Word p_align; }; -/* Values for p_type. */ +/* Values for p_type. See [ELF1] 2-3. */ #define PT_NULL 0 /* Ignore. */ #define PT_LOAD 1 /* Loadable segment. */ #define PT_DYNAMIC 2 /* Dynamic linking info. */ @@ -67,12 +69,11 @@ struct Elf32_Phdr #define PT_PHDR 6 /* Program header table. */ #define PT_STACK 0x6474e551 /* Stack segment. */ -/* Flags for p_flags. */ +/* Flags for p_flags. See [ELF3] 2-3 and 2-4. */ #define PF_X 1 /* Executable. */ #define PF_W 2 /* Writable. */ #define PF_R 4 /* Readable. */ -static bool install_page (struct thread *, void *upage, void *kpage); static bool load_segment (struct thread *, struct file *, const struct Elf32_Phdr *); static bool setup_stack (struct thread *); @@ -83,12 +84,14 @@ static bool setup_stack (struct thread *); printk ("addrspace_load: %s: ", filename); \ printk MSG; \ printk ("\n"); \ - goto error; \ + goto done; \ } while (0) +/* Loads an ELF executable from FILENAME into T, + and stores the executable's entry point into *START. + Returns true if successful, false otherwise. */ bool -addrspace_load (struct thread *t, const char *filename, - void (**start) (void)) +addrspace_load (struct thread *t, const char *filename, void (**start) (void)) { struct Elf32_Ehdr ehdr; struct file file; @@ -153,21 +156,23 @@ addrspace_load (struct thread *t, const char *filename, break; case PT_LOAD: if (!load_segment (t, &file, &phdr)) - goto error; + goto done; break; } } /* Set up stack. */ if (!setup_stack (t)) - goto error; + goto done; /* Start address. */ *start = (void (*) (void)) ehdr.e_entry; success = true; - error: + done: + /* We arrive here whether the load is successful or not. + We can distinguish based on `success'. */ if (file_open) file_close (&file); if (!success) @@ -175,6 +180,8 @@ addrspace_load (struct thread *t, const char *filename, return success; } +/* Destroys the user address space in T and frees all of its + resources. */ void addrspace_destroy (struct thread *t) { @@ -185,46 +192,42 @@ addrspace_destroy (struct thread *t) } } +/* Sets up the CPU for running user code in thread T, if any. */ void addrspace_activate (struct thread *t) { ASSERT (t != NULL); - + + /* Activate T's page tables. */ pagedir_activate (t->pagedir); + + /* Set T's kernel stack for use in processing interrupts. */ tss_set_esp0 ((uint8_t *) t + PGSIZE); } /* addrspace_load() helpers. */ -static bool -install_page (struct thread *t, void *upage, void *kpage) -{ - /* Verify that there's not already a page at that virtual - address, then map our page there. */ - if (pagedir_get_page (t->pagedir, upage) == NULL - && pagedir_set_page (t->pagedir, upage, kpage, true)) - return true; - else - { - palloc_free (kpage); - return false; - } -} +static bool install_page (struct thread *, void *upage, void *kpage); +/* Loads the segment described by PHDR from FILE into thread T's + user address space. Return true if successful, false + otherwise. */ static bool load_segment (struct thread *t, struct file *file, const struct Elf32_Phdr *phdr) { - void *start, *end; - uint8_t *upage; - off_t filesz_left; + void *start, *end; /* Page-rounded segment start and end. */ + uint8_t *upage; /* Iterator from start to end. */ + off_t filesz_left; /* Bytes left of file data (as opposed to + zero-initialized bytes). */ ASSERT (t != NULL); ASSERT (file != NULL); ASSERT (phdr != NULL); ASSERT (phdr->p_type == PT_LOAD); - /* p_offset and p_vaddr must be congruent modulo PGSIZE. */ + /* [ELF1] 2-2 says that p_offset and p_vaddr must be congruent + modulo PGSIZE. */ if (phdr->p_offset % PGSIZE != phdr->p_vaddr % PGSIZE) { printk ("%#08"PE32Ox" and %#08"PE32Ax" not congruent modulo %#x\n", @@ -232,7 +235,8 @@ load_segment (struct thread *t, struct file *file, return false; } - /* p_memsz must be at least as big as p_filesz. */ + /* [ELF1] 2-3 says that p_memsz must be at least as big as + p_filesz. */ if (phdr->p_memsz < phdr->p_filesz) { printk ("p_memsz (%08"PE32Wx") < p_filesz (%08"PE32Wx")\n", @@ -240,7 +244,10 @@ load_segment (struct thread *t, struct file *file, return false; } - /* Validate virtual memory region to be mapped. */ + /* Validate virtual memory region to be mapped. + The region must both start and end within the user address + space range starting at 0 and ending at PHYS_BASE (typically + 3 GB == 0xc0000000). */ start = pg_round_down ((void *) phdr->p_vaddr); end = pg_round_up ((void *) (phdr->p_vaddr + phdr->p_memsz)); if (start >= PHYS_BASE || end >= PHYS_BASE || end < start) @@ -250,38 +257,68 @@ load_segment (struct thread *t, struct file *file, return false; } + /* Load the segment page-by-page into memory. */ filesz_left = phdr->p_filesz + (phdr->p_vaddr & PGMASK); file_seek (file, ROUND_DOWN (phdr->p_offset, PGSIZE)); for (upage = start; upage < (uint8_t *) end; upage += PGSIZE) { + /* We want to read min(PGSIZE, filesz_left) bytes from the + file into the page and zero the rest. */ size_t read_bytes = filesz_left >= PGSIZE ? PGSIZE : filesz_left; size_t zero_bytes = PGSIZE - read_bytes; uint8_t *kpage = palloc_get (0); if (kpage == NULL) return false; - if (file_read (file, kpage, read_bytes) != (int) read_bytes) - return false; + /* Do the reading and zeroing. */ + if (file_read (file, kpage, read_bytes) != (int) read_bytes) + { + palloc_free (kpage); + return false; + } memset (kpage + read_bytes, 0, zero_bytes); filesz_left -= read_bytes; - if (!install_page (t, upage, kpage)) - return false; + /* Add the page to the process's address space. */ + if (!install_page (t, upage, kpage)) + { + palloc_free (kpage); + return false; + } } return true; } +/* Create a minimal stack for T by mapping a zeroed page at the + top of user virtual memory. */ static bool setup_stack (struct thread *t) { - uint8_t *kpage = palloc_get (PAL_ZERO); - if (kpage == NULL) + uint8_t *kpage; + bool success = false; + + kpage = palloc_get (PAL_ZERO); + if (kpage != NULL) { - printk ("failed to allocate process stack\n"); - return false; + success = install_page (t, ((uint8_t *) PHYS_BASE) - PGSIZE, kpage); + if (!success) + palloc_free (kpage); } + else + printk ("failed to allocate process stack\n"); - return install_page (t, ((uint8_t *) PHYS_BASE) - PGSIZE, kpage); + return success; } +/* Adds a mapping from user virtual address UPAGE to kernel + virtual address KPAGE to T's page tables. Fails if UPAGE is + already mapped or if memory allocation fails. */ +static bool +install_page (struct thread *t, void *upage, void *kpage) +{ + /* Verify that there's not already a page at that virtual + address, then map our page there. */ + return (pagedir_get_page (t->pagedir, upage) == NULL + && pagedir_set_page (t->pagedir, upage, kpage, true)); +}