Eu tenho certeza que meu código em C

é perfeito

Guilherme Polo

14 de setembro de 2011

2nd D

raft

``Somebody told me that in basketball you can't hold the ball and run. I got a basketball and tried it and it worked just fine. He obviously didn't understand basketball.’’ Roger Miller

int i;int *x;

x = (int *)malloc(10 * sizeof(int));

for (i = 0; i < 10; i++) { x[i]++;}for (i = 0; i < 10; i++) { printf("%d: %d\n", i, x[i]);}free(x);

2011-247

int i;int *x;

x = (int *)malloc(10 * sizeof(int));

for (i = 0; i < 10; i++) { x[i]++;}for (i = 0; i < 10; i++) { printf("%d: %d\n", i, x[i]);}free(x);

http://c-faq.com/malloc/cast.html

2011-247

int i;int *x;

x = (int *)malloc(10 * sizeof(int));

for (i = 0; i < 10; i++) { x[i]++;}for (i = 0; i < 10; i++) { printf("%d: %d\n", i, x[i]);}free(x);

*x

http://c-faq.com/aryptr/fn33.html

2011-247

int i;int *x;

x = (int *)malloc(10 * sizeof(int));

for (i = 0; i < 10; i++) { x[i]++;}for (i = 0; i < 10; i++) { printf("%d: %d\n", i, x[i]);}free(x);

*x

x[i] nunca foi inicializado

?

2011-247

int i;int *x;

x = (int *)malloc(10 * sizeof(int));

for (i = 0; i < 10; i++) { x[i]++;}for (i = 0; i < 10; i++) { printf("%d: %d\n", i, x[i]);}free(x);

*x

memset(x, 0, 10 * sizeof(*x));

2011-247

int i;int *x;

x = (int *)malloc(10 * sizeof(int));

for (i = 0; i < 10; i++) { x[i]++;}for (i = 0; i < 10; i++) { printf("%d: %d\n", i, x[i]);}free(x);

*x

memset(x, 0, 10 * sizeof(*x));

2011-247

void f(int **x) { if (*x == NULL) { *x = malloc(sizeof(**x)); } **x = 10;}

...

int *x;f(&x);free(x);

2011-247

void f(int **x) { if (*x == NULL) { *x = malloc(sizeof(**x)); } **x = 10;}

...

int *x;f(&x);free(x);

2011-247

void f(int **x) { if (*x == NULL) { *x = malloc(sizeof(**x)); } **x = 10;}

...

int *x;f(&x);free(x);

memória nunca foi alocada

2011-247

void f(int **x) { if (*x == NULL) { *x = malloc(sizeof(**x)); } **x = 10;}

...

int *x;f(&x);free(x);

x = NULL;

2011-247

void f(int **x) { if (*x == NULL) { *x = malloc(sizeof(**x)); } **x = 10;}

...

int *x;f(&x);free(x);

x = NULL;

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int **x, i, j;

x = malloc(sizeof(int) * 10);for (i = 0; i < 10; i++) { x[i] = malloc(sizeof(int) * 5);}for (i = 0; i < 10; i++) { free(x[i]);}

2011-247

int **x, i, j;

x = malloc(sizeof(int) * 10);for (i = 0; i < 10; i++) { x[i] = malloc(sizeof(int) * 5);}for (i = 0; i < 10; i++) { free(x[i]);}

int*

2011-247

int **x, i, j;

x = malloc(sizeof(int) * 10);for (i = 0; i < 10; i++) { x[i] = malloc(sizeof(int) * 5);}for (i = 0; i < 10; i++) { free(x[i]);}

int*

*x

2011-247

int **x, i, j;

x = malloc(sizeof(int) * 10);for (i = 0; i < 10; i++) { x[i] = malloc(sizeof(int) * 5);}for (i = 0; i < 10; i++) { free(x[i]);}

int*

*x

**x

2011-247

int **x, i, j;

x = malloc(sizeof(int) * 10);for (i = 0; i < 10; i++) { x[i] = malloc(sizeof(int) * 5);}for (i = 0; i < 10; i++) { free(x[i]);}

int*

*x

**x

free(x);

2011-247

int **x, i, j;

x = malloc(sizeof(int) * 10);for (i = 0; i < 10; i++) { x[i] = malloc(sizeof(int) * 5);}for (i = 0; i < 10; i++) { free(x[i]);}

int*

*x

**x

free(x);

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int i, j, k, l, max, *t;max = 10;t = malloc(max * sizeof(*t));for (i = 0; i < max; i++) t[i] = max - i;k = 0;while (1) { t[k]--; for (j=k-1, l=0; j>=0 && (t[k]-l)>0; j--,l++) t[j]++; ++j; if (t[j] > 0) k = j; else k++; if (k > max) break;}free(t);

2011-247

int i, j, k, l, max, *t;max = 10;t = malloc(max * sizeof(*t));for (i = 0; i < max; i++) t[i] = max - i;k = 0;while (1) { t[k]--; for (j=k-1, l=0; j>=0 && (t[k]-l)>0; j--,l++) t[j]++; ++j; if (t[j] > 0) k = j; else k++; if (k > max) break;}free(t);

permite acessar t[10]

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int i, j, k, l, max, *t;max = 10;t = malloc(max * sizeof(*t));for (i = 0; i < max; i++) t[i] = max - i;k = 0;while (1) { t[k]--; for (j=k-1, l=0; j>=0 && (t[k]-l)>0; j--,l++) t[j]++; ++j; if (t[j] > 0) k = j; else k++; if (k > max) break;}free(t);

permite acessar t[10] , que é o sentinela

2011-247

int i, j, k, l, max, *t;max = 10;t = malloc(max * sizeof(*t));for (i = 0; i < max; i++) t[i] = max - i;k = 0;while (1) { t[k]--; for (j=k-1, l=0; j>=0 && (t[k]-l)>0; j--,l++) t[j]++; ++j; if (t[j] > 0) k = j; else k++; if (k > max) break;}free(t);

permite acessar t[10] , que é o sentinela

(max + 1)

2011-247

int i, j, k, l, max, *t;max = 10;t = malloc(max * sizeof(*t));for (i = 0; i < max; i++) t[i] = max - i;k = 0;while (1) { t[k]--; for (j=k-1, l=0; j>=0 && (t[k]-l)>0; j--,l++) t[j]++; ++j; if (t[j] > 0) k = j; else k++; if (k > max) break;}free(t);

permite acessar t[10] , que é o sentinela

(max + 1)

t[10] não foi inicializado

2011-247

int i, j, k, l, max, *t;max = 10;t = malloc(max * sizeof(*t));for (i = 0; i < max; i++) t[i] = max - i;k = 0;while (1) { t[k]--; for (j=k-1, l=0; j>=0 && (t[k]-l)>0; j--,l++) t[j]++; ++j; if (t[j] > 0) k = j; else k++; if (k > max) break;}free(t);

(max + 1)<=

2011-247

int i, j, k, l, max, *t;max = 10;t = malloc(max * sizeof(*t));for (i = 0; i < max; i++) t[i] = max - i;k = 0;while (1) { t[k]--; for (j=k-1, l=0; j>=0 && (t[k]-l)>0; j--,l++) t[j]++; ++j; if (t[j] > 0) k = j; else k++; if (k > max) break;}free(t);

(max + 1)<=

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2011-257

struct s { enum {a, b, c} t; union { int i; } v;};

int i, max = 0;struct s *x = malloc(100 * sizeof(*x));for (i = 0; i < 100; i++) { x[i].t = random() % 3; if (x[i].t == a) x[i].v.i = i;}for (i = 0; i < 100; i++) { max = (x[i].v.i > max) ? x[i].v.i : max;}

...

2011-257

struct s { enum {a, b, c} t; union { int i; } v;};

int i, max = 0;struct s *x = malloc(100 * sizeof(*x));for (i = 0; i < 100; i++) { x[i].t = random() % 3; if (x[i].t == a) x[i].v.i = i;}for (i = 0; i < 100; i++) { max = (x[i].v.i > max) ? x[i].v.i : max;}

...Conteúdo potencialmentenão inicializado

2011-257

struct s { enum {a, b, c} t; union { int i; } v;};

int i, max = 0;struct s *x = malloc(100 * sizeof(*x));for (i = 0; i < 100; i++) { x[i].t = random() % 3; if (x[i].t == a) x[i].v.i = i;}for (i = 0; i < 100; i++) { if (x[i].t == a) max = (x[i].v.i > max) ? x[i].v.i : max;}

...

2011-257

struct s { enum {a, b, c} t; union { int i; } v;};

int i, max = 0;struct s *x = malloc(100 * sizeof(*x));for (i = 0; i < 100; i++) { x[i].t = random() % 3; if (x[i].t == a) x[i].v.i = i;}for (i = 0; i < 100; i++) { if (x[i].t == a) max = (x[i].v.i > max) ? x[i].v.i : max;}

...

Outras recomendações

• Diferentemente dos exemplos exibidos, verifique todos os retornos

• Crie funções (com nomenclatura consistente) que fazem a verificação

• malloc Malloc, scanf Scanf, ...

• Utilize Valgrind não somente para verificar por memory leak

→ →

Valgrind vs.clang + SAFECode 1 #include <stdlib.h> 2 3 int 4 main(void) 5 { 6 int i, *x; 7 8 x = malloc(10 * sizeof *x); 9 for (i = -5; i < 15; i++) {10 x[i] = 0;11 }12 13 return 0;14 }

broken.c

Valgrind$ gcc -Wall -ansi -pedantic -m32 -g -o broken broken.c

$ ./broken

$

Código executou sem problemas!Se a frase do Roger Miller não tinha feito sentido, volte para o começo destes slides e a releia

Valgrind

$ valgrind ./broken<Mensagem inicial removida>==17920== ==17920== Invalid write of size 4==17920== at 0x1F6D: main (broken.c:10)==17920== Address 0x24f34c is not stack'd, malloc'd or (recently) free'd==17920== <Continua ..>

Valgrind

$ valgrind ./broken<Mensagem inicial removida>==17920== ==17920== Invalid write of size 4==17920== at 0x1F6D: main (broken.c:10)==17920== Address 0x24f34c is not stack'd, malloc'd or (recently) free'd==17920== <Continua ..>

PID

x[i] = 0;

estamos mexendo em algo que não nos pertence

Valgrind<Continua ..>==17959== ==17959== HEAP SUMMARY:==17959== in use at exit: 360 bytes in 8 blocks==17959== total heap usage: 8 allocs, 0 frees, 360 bytes allocated==17959== ==17959== LEAK SUMMARY:==17959== definitely lost: 40 bytes in 1 blocks==17959== indirectly lost: 0 bytes in 0 blocks==17959== possibly lost: 0 bytes in 0 blocks==17959== still reachable: 320 bytes in 7 blocks==17959== suppressed: 0 bytes in 0 blocks<Continua ..>

Valgrind<Continua ..>==17959== ==17959== HEAP SUMMARY:==17959== in use at exit: 360 bytes in 8 blocks==17959== total heap usage: 8 allocs, 0 frees, 360 bytes allocated==17959== ==17959== LEAK SUMMARY:==17959== definitely lost: 40 bytes in 1 blocks==17959== indirectly lost: 0 bytes in 0 blocks==17959== possibly lost: 0 bytes in 0 blocks==17959== still reachable: 320 bytes in 7 blocks==17959== suppressed: 0 bytes in 0 blocks<Continua ..>

código nãochamou free

Valgrind<Continua ..>==17959== Rerun with --leak-check=full to see details of leaked memory==17959== ==17959== For counts of detected and suppressed errors, rerun with: -v==17959== ERROR SUMMARY: 10 errors from 1 contexts (suppressed: 0 from 0)

Valgrind<Continua ..>==17959== Rerun with --leak-check=full to see details of leaked memory==17959== ==17959== For counts of detected and suppressed errors, rerun with: -v==17959== ERROR SUMMARY: 10 errors from 1 contexts (suppressed: 0 from 0)

Quais posições invalidas foram acessadas ?-5, -4, -3, -2, -1, 10, 11, 12, 13, 14. Total: 10

clang + SAFECode$ clang -g -fmemsafety -o broken.o -c broken.c$ clang -g -o broken broken.o -lsc_dbg_rt \ -lpoolalloc_bitmap -lstdc++$ ./broken<Próximo slide..>

clang + SAFECodeSAFECode:Violation Type 0x6 when accessing 0x10010022c at IP=0x100001ca8

=======+++++++ SAFECODE RUNTIME ALERT +++++++======== Error type : Load/Store Error= Faulting pointer : 0x10010022c= Program counter : 0x100001ca8= Fault PC Source : broken.c:10== Object allocated at PC : 0x100001b2d= Allocated in Source File : broken.c:8= Object allocation sequence number : 1= Object start : 0x100100240= Object length : 0x28

<E várias outras parecidas para cada acesso inválido>

clang + SAFECodeSAFECode:Violation Type 0x6 when accessing 0x10010022c at IP=0x100001ca8

=======+++++++ SAFECODE RUNTIME ALERT +++++++======== Error type : Load/Store Error= Faulting pointer : 0x10010022c= Program counter : 0x100001ca8= Fault PC Source : broken.c:10== Object allocated at PC : 0x100001b2d= Allocated in Source File : broken.c:8= Object allocation sequence number : 1= Object start : 0x100100240= Object length : 0x28

<E várias outras parecidas para cada acesso inválido>

estamos mexendo em algo que não

nos pertence

endereço que não deveria ter sido

acessado

onde deu problema

clang + SAFECodeSAFECode:Violation Type 0x6 when accessing 0x10010022c at IP=0x100001ca8

=======+++++++ SAFECODE RUNTIME ALERT +++++++======== Error type : Load/Store Error= Faulting pointer : 0x10010022c= Program counter : 0x100001ca8= Fault PC Source : broken.c:10== Object allocated at PC : 0x100001b2d= Allocated in Source File : broken.c:8= Object allocation sequence number : 1= Object start : 0x100100240= Object length : 0x28

<E várias outras parecidas para cada acesso inválido>x = malloc(10 * sizeof *x);0x28 = (40)10 bytes foram alocados

endereço inicial da região alocada

clang + SAFECodeSAFECode:Violation Type 0x6 when accessing 0x10010022c at IP=0x100001ca8

=======+++++++ SAFECODE RUNTIME ALERT +++++++======== Error type : Load/Store Error= Faulting pointer : 0x10010022c= Program counter : 0x100001ca8= Fault PC Source : broken.c:10== Object allocated at PC : 0x100001b2d= Allocated in Source File : broken.c:8= Object allocation sequence number : 1= Object start : 0x100100240= Object length : 0x28

<E várias outras parecidas para cada acesso inválido>

Valgrind vs.clang + SAFECode

De modo geral, a segunda opção fornece alguns detalhes extras para casos de acessos fora dos limites

Para acessos inválidos dentro dos limites, a versão atual não reporta erros

O exemplo utilizado não contempla esta situação

``Programmers waste enormous amounts of time thinking about, or worrying about, the speed of noncritical parts of their programs, and these attempts at efficiency actually have a strong negative impact when debugging and maintenance are considered. We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%.’’ Donald E. Knuth

struct node { struct node *next; };

voidappend(struct node *l, struct node *n){ while (l->next) { l = l->next; } l->next = n;}

... int i;struct node *l = calloc(1, sizeof(*l));

for (i = 0; i < 1000000; i++) append(l, calloc(1, sizeof(*l));...

2011-247

struct node { struct node *next; };

voidappend(struct node *l, struct node *n){ while (l->next) { l = l->next; } l->next = n;}

... int i;struct node *l = calloc(1, sizeof(*l));

for (i = 0; i < 1000000; i++) append(l, calloc(1, sizeof(*l));...

( )

2011-247

struct node { struct node *next; };

void append(struct node *l, struct node *n){ while (l->next) { l = l->next; } l->next = n; }

...int i;struct node *l = calloc(1, sizeof(*l));

for (i = 0; i < 1000000; i++) append(l, calloc(1, sizeof(*l));...

( )

struct node *

return n;

2011-247

struct node { struct node *next; };

void append(struct node *l, struct node *n){ while (l->next) { l = l->next; } l->next = n; }

...int i;struct node *l = calloc(1, sizeof(*l));

for (i = 0; i < 1000000; i++) append(l, calloc(1, sizeof(*l));...

( )

struct node *

return n;

struct node *end = l;

end2011-247

struct node { struct node *next; };

void append(struct node *l, struct node *n){ while (l->next) { l = l->next; } l->next = n; }

...int i;struct node *l = calloc(1, sizeof(*l));

for (i = 0; i < 1000000; i++) append(l, calloc(1, sizeof(*l));...

struct node *

return n;

struct node *end = l;

end

end =

2011-247

struct node { struct node *next; };

void append(struct node *l, struct node *n){ while (l->next) { l = l->next; } l->next = n; }

...int i;struct node *l = calloc(1, sizeof(*l));

for (i = 0; i < 1000000; i++) append(l, calloc(1, sizeof(*l));...

struct node *

return n;

struct node *end = l;

end

end =

2011-247